A170825 a(n) is the product of the distinct primes of form 6*k-1 that divide n.

1, 1, 1, 1, 5, 1, 1, 1, 1, 5, 11, 1, 1, 1, 5, 1, 17, 1, 1, 5, 1, 11, 23, 1, 5, 1, 1, 1, 29, 5, 1, 1, 11, 17, 5, 1, 1, 1, 1, 5, 41, 1, 1, 11, 5, 23, 47, 1, 1, 5, 17, 1, 53, 1, 55, 1, 1, 29, 59, 5, 1, 1, 1, 1, 5, 11, 1, 17, 23, 5, 71, 1, 1, 1, 5, 1, 11, 1, 1, 5, 1, 41, 83, 1, 85, 1, 29, 11, 89, 5, 1

Offset: 1

Author

N. J. A. Sloane, Dec 25 2009, following a suggestion from Jonathan Vos Post

Keywords

• nonn
• mult
• easy

Links

• Amiram Eldar, Table of n, a(n) for n = 1..10000

Crossrefs

Cf. A007528, A007947, A170819, A343431.

Cf. A140214. - R. J. Mathar, Jan 21 2010

Programs

Maple

A170825 := proc(n) a := 1 ; for p in numtheory[factorset](n) do if p mod 6 = 5 then a := a*p ; end if ; end do ; a ; end proc: seq(A170825(n),n=1..120) ; # R. J. Mathar, Jan 21 2010

Mathematica

Table[Times@@Select[Transpose[FactorInteger[n]][[1]],IntegerQ[(#+1)/6]&],{n,100}] (* Harvey P. Dale, Nov 01 2013 *)

PARI

a(n) = my(f=factor(n)); for(i=1, #f~, f[i,2] = (f[i,1]%6)==5); factorback(f); \\ Michel Marcus, Sep 30 2020

Formula

a(n) = A007947(A343431(n)) = A343431(A007947(n)). - Peter Munn, Jan 15 2022

Extensions

More terms from R. J. Mathar, Jan 21 2010