OFFSET
1,3
MATHEMATICA
a[n_] := Sum[If[GCD[n, k] == 1, StirlingS2[n, k] , 0], {k, 1, n}]; Table[a[n], {n, 1, 25}]
PROG
(PARI) a(n) = sum(k=1, n, if (gcd(n, k)==1, stirling(n, k, 2))); \\ Michel Marcus, May 28 2019
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, May 28 2019
STATUS
approved