OFFSET
0,3
COMMENTS
a(n) is the number of n-ary clones of the "discriminator function" t(x,y,z) defined by t(x,y,z)=x if x != y, t(x,x,z)=z.
For example, one of the 24 clones when n=3 is the function f(x,y,z)=t(t(y,z,x),x,t(x,y,z)), which has the property that f(x,x,x)=x, f(x,x,y)=y, f(x,y,x)=y, f(x,y,y)=x, f(x,y,z)=y when x,y,z are distinct. There are 24 meaningful ways to specify the right-hand sides of these five equations, and each of those functions can be expressed as a term in t.
LINKS
Hugo Pfoertner, Table of n, a(n) for n = 0..7
Alden F. Pixley, The Ternary Discriminator Function in Universal Algebra, Mathematische Annalen, 191 (1971), 167-180.
MATHEMATICA
A373796[n_] := Product[k^StirlingS2[n, k], {k, n}];
Array[A373796, 8, 0] (* Paolo Xausa, Jul 10 2024 *)
PROG
(PARI) a(n)=prod(k=1, n, k^stirling(n, k, 2)) \\ Hugo Pfoertner, Jul 07 2024
CROSSREFS
KEYWORD
nonn
AUTHOR
N. J. A. Sloane, Jul 07 2024, based on an email from Don Knuth, Jul 06 2024.
STATUS
approved