A140210 a(n) = Product_{h == 1 (mod 4) and h|n} h.

1, 1, 1, 1, 5, 1, 1, 1, 9, 5, 1, 1, 13, 1, 5, 1, 17, 9, 1, 5, 21, 1, 1, 1, 125, 13, 9, 1, 29, 5, 1, 1, 33, 17, 5, 9, 37, 1, 13, 5, 41, 21, 1, 1, 2025, 1, 1, 1, 49, 125, 17, 13, 53, 9, 5, 1, 57, 29, 1, 5, 61, 1, 189, 1, 4225, 33, 1, 17, 69, 5, 1, 9, 73, 37, 125, 1, 77, 13, 1, 5, 729, 41, 1, 21

Offset: 1

Author

R. J. Mathar, Jun 27 2008

Keywords

• nonn
• look

Links

• Alois P. Heinz, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007955, A140211, A136655, A140213, A140214, A140215, A136655.

Programs

Maple

with(numtheory):
a:= n-> mul(i, i=select(h-> irem(h, 4)=1, divisors(n))):
seq(a(n), n=1..120);  # Alois P. Heinz, Jul 28 2009

Mathematica

a[n_] := Times @@ Select[Divisors[n], Mod[#, 4] == 1&]; Table[a[n], {n, 1, 120}] (* Jean-François Alcover, Jun 24 2015 *)

PARI

a(n) = my(p=1); fordiv(n, d, if ((d % 4)==1, p*=d)); p; \\ Michel Marcus, Jan 07 2021

Extensions

More terms from Alois P. Heinz, Jul 28 2009