OFFSET
1,1
FORMULA
a(n) = Sum_{ d divides n } ((2*n!)/(d!*((n/d)!)^d)).
a(n) = 2 * A038041(n). - Sean A. Irvine, Jan 05 2021
MAPLE
with(numtheory): for n from 1 to 50 do d := divisors(n): s := 0: for k from 1 to nops(d) do s := s +(2*n!)/(d[k]!*((n/d[k])!)^d[k]) od: printf(`%d, `, s) od:
PROG
(PARI) a(n) = sumdiv(n, d, ((2*n!)/(d!*((n/d)!)^d))); \\ Michel Marcus, Jan 05 2021
CROSSREFS
KEYWORD
nonn
AUTHOR
EXTENSIONS
More terms from James A. Sellers, Feb 19 2001
STATUS
approved