OFFSET
1,2
FORMULA
a(n) = 2 <=> n is prime <=> n in { A000040 }. - Alois P. Heinz, May 10 2019
MAPLE
a:= n-> add(Stirling2(n, d), d=numtheory[divisors](n)):
seq(a(n), n=1..30); # Alois P. Heinz, May 10 2019
MATHEMATICA
a[n_] := a[n] = Sum[StirlingS2[n, d], {d, Divisors[n]}]; Table[a[n], {n, 1, 29}]
PROG
(PARI) a(n) = sumdiv(n, d, stirling(n, d, 2)); \\ Michel Marcus, May 10 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, May 10 2019
STATUS
approved