OFFSET
0,3
COMMENTS
Number of labeled magmas with n elements satisfying the equation x(yz) = xz. - Andrew Howroyd, Apr 24 2023
LINKS
Alois P. Heinz, Table of n, a(n) for n = 0..76
Wikipedia, Kronecker delta
FORMULA
a(n) = n! * [x^n] exp(exp(x)*(Sum_{j=0..n} Stirling2(n,j)*x^j) - delta_{0,n}).
MAPLE
b:= proc(n, k) option remember; `if`(n=0, 1,
add(binomial(n-1, j-1)*j^k*b(n-j, k), j=1..n))
end:
a:= n-> b(n$2):
seq(a(n), n=0..15);
MATHEMATICA
b[n_, k_] := b[n, k] = If[n == 0, 1, Sum[Binomial[n-1, j-1]*j^k*b[n-j, k], {j, 1, n}]];
a[n_] := b[n, n];
Table[a[n], {n, 0, 15}] (* Jean-François Alcover, Jun 01 2018, from Maple *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alois P. Heinz, Dec 16 2016
STATUS
approved