Sedenion

A visualization of a 4D extension to the cubic octonion,[2] showing the 35 triads as hyperplanes through the real ${\displaystyle (e_{0})}$ vertex of the sedenion example given. Note that the only exception is that the triple ${\displaystyle (e_{1})}$, ${\displaystyle (e_{2})}$, ${\displaystyle (e_{3})}$ doesn't form a hyperplane with ${\displaystyle (e_{0})}$.

Like octonions, multiplication of sedenions is neither commutative nor associative. But in contrast to the octonions, the sedenions do not even have the property of being alternative. They do, however, have the property of power associativity, which can be stated as that, for any element x of ${\displaystyle \mathbb {S} }$, the power ${\displaystyle x^{n}}$ is well defined. They are also flexible.

Every sedenion is a linear combination of the unit sedenions ${\displaystyle e_{0}}$, ${\displaystyle e_{1}}$, ${\displaystyle e_{2}}$, ${\displaystyle e_{3}}$, ...,${\displaystyle e_{15}}$, which form a basis of the vector space of sedenions. Every sedenion can be represented in the form

${\displaystyle x=x_{0}e_{0}+x_{1}e_{1}+x_{2}e_{2}+\ldots +x_{14}e_{14}+x_{15}e_{15},\,}$.

Addition and subtraction are defined by the addition and subtraction of corresponding coefficients and multiplication is distributive over addition.

Like other algebras based on the Cayley–Dickson construction, the sedenions contain the algebra they were constructed from. So, they contain the octonions (generated by ${\displaystyle e_{0}}$ to ${\displaystyle e_{7}}$ in the table below), and therefore also the quaternions (generated by ${\displaystyle e_{0}}$ to ${\displaystyle e_{3}}$), complex numbers (generated by ${\displaystyle e_{0}}$ and ${\displaystyle e_{1}}$) and reals (generated by ${\displaystyle e_{0}}$).

The sedenions have a multiplicative identity element ${\displaystyle e_{0}}$ and multiplicative inverses but they are not a division algebra because they have zero divisors. This means that two non-zero sedenions can be multiplied to obtain zero: an example is (${\displaystyle e_{3}}$ + ${\displaystyle e_{10}}$)(${\displaystyle e_{6}}$ − ${\displaystyle e_{15}}$). All hypercomplex number systems after sedenions that are based on the Cayley–Dickson construction contain zero divisors.

A sedenion multiplication table is shown below:

multiplication table

multiplier ${\displaystyle e_{j}}$ ${\displaystyle e_{i}e_{j}}$ ${\displaystyle e_{0}}$ ${\displaystyle e_{1}}$ ${\displaystyle e_{2}}$ ${\displaystyle e_{3}}$ ${\displaystyle e_{4}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{6}}$ ${\displaystyle e_{7}}$ ${\displaystyle e_{8}}$ ${\displaystyle e_{9}}$ ${\displaystyle e_{10}}$ ${\displaystyle e_{11}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{13}}$ ${\displaystyle e_{14}}$ ${\displaystyle e_{15}}$ multiplicand ${\displaystyle e_{i}}$ ${\displaystyle e_{0}}$ ${\displaystyle e_{0}}$ ${\displaystyle e_{1}}$ ${\displaystyle e_{2}}$ ${\displaystyle e_{3}}$ ${\displaystyle e_{4}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{6}}$ ${\displaystyle e_{7}}$ ${\displaystyle e_{8}}$ ${\displaystyle e_{9}}$ ${\displaystyle e_{10}}$ ${\displaystyle e_{11}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{13}}$ ${\displaystyle e_{14}}$ ${\displaystyle e_{15}}$ ${\displaystyle e_{1}}$ ${\displaystyle e_{1}}$ −${\displaystyle e_{0}}$ ${\displaystyle e_{3}}$ −${\displaystyle e_{2}}$ ${\displaystyle e_{5}}$ −${\displaystyle e_{4}}$ −${\displaystyle e_{7}}$ ${\displaystyle e_{6}}$ ${\displaystyle e_{9}}$ −${\displaystyle e_{8}}$ −${\displaystyle e_{11}}$ ${\displaystyle e_{10}}$ −${\displaystyle e_{13}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{15}}$ −${\displaystyle e_{14}}$ ${\displaystyle e_{2}}$ ${\displaystyle e_{2}}$ −${\displaystyle e_{3}}$ −${\displaystyle e_{0}}$ ${\displaystyle e_{1}}$ ${\displaystyle e_{6}}$ ${\displaystyle e_{7}}$ −${\displaystyle e_{4}}$ −${\displaystyle e_{5}}$ ${\displaystyle e_{10}}$ ${\displaystyle e_{11}}$ −${\displaystyle e_{8}}$ −${\displaystyle e_{9}}$ −${\displaystyle e_{14}}$ −${\displaystyle e_{15}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{13}}$ ${\displaystyle e_{3}}$ ${\displaystyle e_{3}}$ ${\displaystyle e_{2}}$ −${\displaystyle e_{1}}$ −${\displaystyle e_{0}}$ ${\displaystyle e_{7}}$ −${\displaystyle e_{6}}$ ${\displaystyle e_{5}}$ −${\displaystyle e_{4}}$ ${\displaystyle e_{11}}$ −${\displaystyle e_{10}}$ ${\displaystyle e_{9}}$ −${\displaystyle e_{8}}$ −${\displaystyle e_{15}}$ ${\displaystyle e_{14}}$ −${\displaystyle e_{13}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{4}}$ ${\displaystyle e_{4}}$ −${\displaystyle e_{5}}$ −${\displaystyle e_{6}}$ −${\displaystyle e_{7}}$ −${\displaystyle e_{0}}$ ${\displaystyle e_{1}}$ ${\displaystyle e_{2}}$ ${\displaystyle e_{3}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{13}}$ ${\displaystyle e_{14}}$ ${\displaystyle e_{15}}$ −${\displaystyle e_{8}}$ −${\displaystyle e_{9}}$ −${\displaystyle e_{10}}$ −${\displaystyle e_{11}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{4}}$ −${\displaystyle e_{7}}$ ${\displaystyle e_{6}}$ −${\displaystyle e_{1}}$ −${\displaystyle e_{0}}$ −${\displaystyle e_{3}}$ ${\displaystyle e_{2}}$ ${\displaystyle e_{13}}$ −${\displaystyle e_{12}}$ ${\displaystyle e_{15}}$ −${\displaystyle e_{14}}$ ${\displaystyle e_{9}}$ −${\displaystyle e_{8}}$ ${\displaystyle e_{11}}$ −${\displaystyle e_{10}}$ ${\displaystyle e_{6}}$ ${\displaystyle e_{6}}$ ${\displaystyle e_{7}}$ ${\displaystyle e_{4}}$ −${\displaystyle e_{5}}$ −${\displaystyle e_{2}}$ ${\displaystyle e_{3}}$ −${\displaystyle e_{0}}$ −${\displaystyle e_{1}}$ ${\displaystyle e_{14}}$ −${\displaystyle e_{15}}$ −${\displaystyle e_{12}}$ ${\displaystyle e_{13}}$ ${\displaystyle e_{10}}$ −${\displaystyle e_{11}}$ −${\displaystyle e_{8}}$ ${\displaystyle e_{9}}$ ${\displaystyle e_{7}}$ ${\displaystyle e_{7}}$ −${\displaystyle e_{6}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{4}}$ −${\displaystyle e_{3}}$ −${\displaystyle e_{2}}$ ${\displaystyle e_{1}}$ −${\displaystyle e_{0}}$ ${\displaystyle e_{15}}$ ${\displaystyle e_{14}}$ −${\displaystyle e_{13}}$ −${\displaystyle e_{12}}$ ${\displaystyle e_{11}}$ ${\displaystyle e_{10}}$ −${\displaystyle e_{9}}$ −${\displaystyle e_{8}}$ ${\displaystyle e_{8}}$ ${\displaystyle e_{8}}$ −${\displaystyle e_{9}}$ −${\displaystyle e_{10}}$ −${\displaystyle e_{11}}$ −${\displaystyle e_{12}}$ −${\displaystyle e_{13}}$ −${\displaystyle e_{14}}$ −${\displaystyle e_{15}}$ −${\displaystyle e_{0}}$ ${\displaystyle e_{1}}$ ${\displaystyle e_{2}}$ ${\displaystyle e_{3}}$ ${\displaystyle e_{4}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{6}}$ ${\displaystyle e_{7}}$ ${\displaystyle e_{9}}$ ${\displaystyle e_{9}}$ ${\displaystyle e_{8}}$ −${\displaystyle e_{11}}$ ${\displaystyle e_{10}}$ −${\displaystyle e_{13}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{15}}$ −${\displaystyle e_{14}}$ −${\displaystyle e_{1}}$ −${\displaystyle e_{0}}$ −${\displaystyle e_{3}}$ ${\displaystyle e_{2}}$ −${\displaystyle e_{5}}$ ${\displaystyle e_{4}}$ ${\displaystyle e_{7}}$ −${\displaystyle e_{6}}$ ${\displaystyle e_{10}}$ ${\displaystyle e_{10}}$ ${\displaystyle e_{11}}$ ${\displaystyle e_{8}}$ −${\displaystyle e_{9}}$ −${\displaystyle e_{14}}$ −${\displaystyle e_{15}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{13}}$ −${\displaystyle e_{2}}$ ${\displaystyle e_{3}}$ −${\displaystyle e_{0}}$ −${\displaystyle e_{1}}$ −${\displaystyle e_{6}}$ −${\displaystyle e_{7}}$ ${\displaystyle e_{4}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{11}}$ ${\displaystyle e_{11}}$ −${\displaystyle e_{10}}$ ${\displaystyle e_{9}}$ ${\displaystyle e_{8}}$ −${\displaystyle e_{15}}$ ${\displaystyle e_{14}}$ −${\displaystyle e_{13}}$ ${\displaystyle e_{12}}$ −${\displaystyle e_{3}}$ −${\displaystyle e_{2}}$ ${\displaystyle e_{1}}$ −${\displaystyle e_{0}}$ −${\displaystyle e_{7}}$ ${\displaystyle e_{6}}$ −${\displaystyle e_{5}}$ ${\displaystyle e_{4}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{12}}$ ${\displaystyle e_{13}}$ ${\displaystyle e_{14}}$ ${\displaystyle e_{15}}$ ${\displaystyle e_{8}}$ −${\displaystyle e_{9}}$ −${\displaystyle e_{10}}$ −${\displaystyle e_{11}}$ −${\displaystyle e_{4}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{6}}$ ${\displaystyle e_{7}}$ −${\displaystyle e_{0}}$ −${\displaystyle e_{1}}$ −${\displaystyle e_{2}}$ −${\displaystyle e_{3}}$ ${\displaystyle e_{13}}$ ${\displaystyle e_{13}}$ −${\displaystyle e_{12}}$ ${\displaystyle e_{15}}$ −${\displaystyle e_{14}}$ ${\displaystyle e_{9}}$ ${\displaystyle e_{8}}$ ${\displaystyle e_{11}}$ −${\displaystyle e_{10}}$ −${\displaystyle e_{5}}$ −${\displaystyle e_{4}}$ ${\displaystyle e_{7}}$ −${\displaystyle e_{6}}$ ${\displaystyle e_{1}}$ −${\displaystyle e_{0}}$ ${\displaystyle e_{3}}$ −${\displaystyle e_{2}}$ ${\displaystyle e_{14}}$ ${\displaystyle e_{14}}$ −${\displaystyle e_{15}}$ −${\displaystyle e_{12}}$ ${\displaystyle e_{13}}$ ${\displaystyle e_{10}}$ −${\displaystyle e_{11}}$ ${\displaystyle e_{8}}$ ${\displaystyle e_{9}}$ −${\displaystyle e_{6}}$ −${\displaystyle e_{7}}$ −${\displaystyle e_{4}}$ ${\displaystyle e_{5}}$ ${\displaystyle e_{2}}$ −${\displaystyle e_{3}}$ −${\displaystyle e_{0}}$ ${\displaystyle e_{1}}$ ${\displaystyle e_{15}}$ ${\displaystyle e_{15}}$ ${\displaystyle e_{14}}$ −${\displaystyle e_{13}}$ −${\displaystyle e_{12}}$ ${\displaystyle e_{11}}$ ${\displaystyle e_{10}}$ −${\displaystyle e_{9}}$ ${\displaystyle e_{8}}$ −${\displaystyle e_{7}}$ ${\displaystyle e_{6}}$ −${\displaystyle e_{5}}$ −${\displaystyle e_{4}}$ ${\displaystyle e_{3}}$ ${\displaystyle e_{2}}$ −${\displaystyle e_{1}}$ −${\displaystyle e_{0}}$

Moreno (1998) showed that the space of pairs of norm-one sedenions that multiply to zero is homeomorphic to the compact form of the exceptional Lie group G₂. (Note that in his paper, a "zero divisor" means a pair of elements that multiply to zero.)

Sedenion neural networks provide a means of efficient and compact expression in machine learning applications and were used in solving multiple time series forecasting problems.[3]

• Pfister's sixteen-square identity
• Hypercomplex number
• Split-complex number

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• Baez, John C. (2002). "The Octonions". Bulletin of the American Mathematical Society. New Series. 39 (2): 145–205. arXiv:math/0105155. doi:10.1090/S0273-0979-01-00934-X. MR 1886087.
• Biss, Daniel K.; Christensen, J. Daniel; Dugger, Daniel; Isaksen, Daniel C. (2007). "Large annihilators in Cayley-Dickson algebras II". Boletin de la Sociedad Matematica Mexicana. 3: 269–292. arXiv:math/0702075.
• Kinyon, M.K.; Phillips, J.D.; Vojtěchovský, P. (2007). "C-loops: Extensions and constructions". Journal of Algebra and Its Applications. 6 (1): 1–20. arXiv:math/0412390. CiteSeerX 10.1.1.240.6208. doi:10.1142/S0219498807001990.
• Kivunge, Benard M.; Smith, Jonathan D. H (2004). "Subloops of sedenions" (PDF). Comment. Math. Univ. Carolinae. 45 (2): 295–302.
• Moreno, Guillermo (1998), "The zero divisors of the Cayley–Dickson algebras over the real numbers", Bol. Soc. Mat. Mexicana, Series 3, 4 (1): 13–28, arXiv:q-alg/9710013, Bibcode:1997q.alg....10013G, MR 1625585
• Smith, Jonathan D. H. (1995), "A left loop on the 15-sphere", Journal of Algebra, 176 (1): 128–138, doi:10.1006/jabr.1995.1237, MR 1345298
• L. S. Saoud and H. Al-Marzouqi, "Metacognitive Sedenion-Valued Neural Network and its Learning Algorithm," in IEEE Access, vol. 8, pp. 144823-144838, 2020, doi: 10.1109/ACCESS.2020.3014690.