A056819 a(n) = Product_{k|n} (n+1-k).

1, 2, 3, 12, 5, 120, 7, 280, 63, 540, 11, 83160, 13, 1456, 2145, 28080, 17, 636480, 19, 1136960, 5985, 5544, 23, 1070845776, 525, 9100, 12825, 6237000, 29, 5320224000, 31, 12226400, 23529, 20196, 31465, 582876756000, 37, 28120, 38961, 44639955360

Offset: 1

Author

Leroy Quet, Sep 01 2000

Keywords

• nonn
• easy

Examples

			a(6) = (6+1-1) *(6+1-2) *(6+1-3) *(6+1-6) = 6 *5 *4 *1 = 120, since the positive divisors of 6 are 1, 2, 3, 6.
		

Links

• John Tyler Rascoe, Table of n, a(n) for n = 1..2000

Programs

Mathematica

a[n_] := Times @@ ((n + 1 - # &) /@ Divisors[n]); Array[a, 40] (* Jean-François Alcover, Sep 30 2016 *)

PARI

a(n) = my(d=divisors(n)); prod(k=1, #d, n+1-d[k]); \\ Michel Marcus, Sep 30 2016

Formula

a(p) = p, for p prime. - Michel Marcus, Sep 30 2016