OFFSET
1,4
COMMENTS
A ring without 1 is still a ring, although sometimes called a rng, or a non-unital ring, or a pseudo-ring (see Wikipedia links).
LINKS
EXAMPLE
a(1) = 0 because the only ring with 1 element is the zero ring (see link) with the element 0, and for this ring, 0 and 1 coincide.
a(3) = 1 because the Matrix ring with 3 elements with coefficients from Z/3Z:
(0 0) (0 0) (0 0)
0 = (0 0), a = (1 0), b = (2 0)
is without 1 (note this ring is commutative) and there is no other such ring with 3 elements and without 1, hence a(3) = 1.
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Bernard Schott, Mar 12 2021
STATUS
approved