A170817 a(n) = product of distinct primes of form 4k+1 that divide n.

1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 1, 1, 13, 1, 5, 1, 17, 1, 1, 5, 1, 1, 1, 1, 5, 13, 1, 1, 29, 5, 1, 1, 1, 17, 5, 1, 37, 1, 13, 5, 41, 1, 1, 1, 5, 1, 1, 1, 1, 5, 17, 13, 53, 1, 5, 1, 1, 29, 1, 5, 61, 1, 1, 1, 65, 1, 1, 17, 1, 5, 1, 1, 73, 37, 5, 1, 1, 13, 1, 5, 1, 41, 1, 1, 85, 1, 29, 1

Offset

1,5

Links

Harvey P. Dale, Table of n, a(n) for n = 1..1000

Maple

a:= n-> mul (i, i=map (x-> x[1], select (x-> isprime (x[1]) and irem (x[1], 4)=1, ifactors(n)[2]))): seq (a(n), n=1..120);

Mathematica

Table[Times@@Select[Transpose[FactorInteger[n]][[1]], Mod[#, 4]==1&], {n, 90}] (* Harvey P. Dale, Dec 07 2012 *)

Prog

(PARI) a(n) = {my(f = factor(n)); prod(i = 1, #f~, if(f[i, 1] % 4 == 1, f[i, 1], 1)); } \\ Amiram Eldar, Jun 09 2025

Crossrefs

Cf. A170818, A170819, A097706, A083025, A170824, A170825.

Sequence in context: A351084 A135469 A348735 * A170818 A046622 A170825

Adjacent sequences: A170814 A170815 A170816 * A170818 A170819 A170820

Keyword

nonn,mult,easy

Author

N. J. A. Sloane, Dec 22 2009

Extensions

Corrected and extended with Maple program by Alois P. Heinz, Dec 23 2009

Status

approved