OFFSET
0,2
COMMENTS
a(n) is the number of binary relations R on {1, 2, ..., n} such that the reflexive, symmetric, and transitive closure of R is the trivial relation.
LINKS
T. D. Noe, Table of n, a(n) for n = 0..30
FORMULA
E.g.f.: 1+log( Sum_{n >= 0} 2^(n^2)*x^n/n! ).
MAPLE
a:= n-> n!*coeff(series(1+log(add(2^(i^2)*x^i/i!, i=0..n)), x, n+1), x, n):
seq(a(n), n=0..30); # Alois P. Heinz, Feb 16 2011
MATHEMATICA
nn = 20; a = Sum[2^(n^2) x^n/n!, {n, 0, nn}]; Range[0, nn]! CoefficientList[Series[Log[a] + 1, {x, 0, nn}], x] (* Geoffrey Critzer, Oct 17 2011 *)
PROG
(PARI) v=Vec(1+log(sum(n=0, 10, 2^(n^2)*x^n/n!))); for(i=1, #v, v[i]*=(i-1)!); v \\ Charles R Greathouse IV, Feb 14 2011
CROSSREFS
KEYWORD
easy,nonn
AUTHOR
Vladeta Jovovic, Jul 12 2001
STATUS
approved