OFFSET
0,3
LINKS
Vincenzo Librandi, Table of n, a(n) for n = 0..100
R. J. Clarke, Covering a set by subsets, Discrete Math., 81 (1990), 147-152.
FORMULA
E.g.f.: Sum_{n>=0} (exp(x)-1)^n*exp(x*(2^n-n-1)), cf. A046165. - Vladeta Jovovic, Sep 01 2005
MATHEMATICA
a[0] = 1; a[n_] := Sum[ (-1)^i*Binomial[k, i]*(2^k-1-i)^n, {k, 0, n}, {i, 0, k} ]; Table[a[n], {n, 0, 15}] (* Jean-François Alcover, Jan 27 2012, after Michael Somos *)
PROG
(PARI) {a(n)=sum(k=0, n, sum(i=0, k, (-1)^i*binomial(k, i)*(2^k-1-i)^n))} /* Michael Somos, Oct 16 2006 */
CROSSREFS
KEYWORD
nonn,easy,nice
AUTHOR
STATUS
approved