A140211 a(n) = Product_{d == 3 (mod 4) and d|n} d.

1, 1, 3, 1, 1, 3, 7, 1, 3, 1, 11, 3, 1, 7, 45, 1, 1, 3, 19, 1, 21, 11, 23, 3, 1, 1, 81, 7, 1, 45, 31, 1, 33, 1, 245, 3, 1, 19, 117, 1, 1, 21, 43, 11, 45, 23, 47, 3, 7, 1, 153, 1, 1, 81, 605, 7, 57, 1, 59, 45, 1, 31, 1323, 1, 1, 33, 67, 1, 69, 245, 71, 3, 1, 1, 3375, 19, 77, 117, 79, 1, 81, 1

Offset: 1

Author

R. J. Mathar, Jun 27 2008

Keywords

• nonn
• easy

Links

• J. Mulder, Table of n, a(n) for n = 1..20000

Crossrefs

Cf. A140210, A007955.

Programs

Maple

A140211 := proc(n)
    a := 1;
    for d in numtheory[divisors](n) do
        if modp(d,4) = 3 then
            a := a*d ;
        end if;
    end do:
    a;
end proc: # R. J. Mathar, Dec 15 2015

Mathematica

ListProduct[lst_] := Fold[Times, 1, lst] lst = {}; For[n = 1, n <= 1000, n++, AppendTo[lst, ListProduct[Select[Divisors[n], Mod[ #, 4] == 3 &]]]] lst (* Jasper Mulder (jasper.mulder(AT)planet.nl), Jul 15 2009 *)

PARI

a(n) = my(p=1); fordiv(n, d, if ((d % 4)==3, p*=d)); p; \\ Michel Marcus, Jan 07 2021

Formula

a(n) | A007955(n). - R. J. Mathar, May 26 2016