OFFSET
1,7
LINKS
Antti Karttunen, Table of n, a(n) for n = 1..10001
FORMULA
a(1) = 1; for n > 1, if A020639(n) = 1 (mod 6), a(n) = A020639(n) * a(A028234(n)), otherwise a(n) = a(A028234(n)). - Antti Karttunen, Jul 09 2017
MAPLE
A170824 := proc(n) a := 1 ; for p in numtheory[factorset](n) do if p mod 6 = 1 then a := a*p ; end if ; end do ; a ; end proc:
A140213 := proc(n) a := 1 ; for p in numtheory[divisors](n) do if p mod 6 = 1 then a := a*p ; end if ; end do ; a ; end proc:
seq(A170824(n), n=1..120) ; # R. J. Mathar, Jan 21 2010
MATHEMATICA
test[p_] := IntegerQ[(p - 1)/6]; a[n_]:= Module[{aux = FactorInteger[n]}, Product[If[test[aux[[i, 1]]], aux[[i, 1]], 1], {i, Length[aux]}]]; Table[a[n], {i, 1, 200}] (* Jose Grau, Feb 16 2010 *)
Table[Times@@Select[Transpose[FactorInteger[n]][[1]], IntegerQ[(#-1)/6]&], {n, 100}] (* Harvey P. Dale, Jul 29 2013 *)
PROG
(Scheme) (define (A170824 n) (if (= 1 n) n (* (if (= 1 (modulo (A020639 n) 6)) (A020639 n) 1) (A170824 (A028234 n))))) ;; Antti Karttunen, Jul 09 2017
(PARI) a(n) = my(f=factor(n)); prod(k=1, #f~, if (((p=f[k, 1])%6) == 1, p, 1)); \\ Michel Marcus, Jul 10 2017
CROSSREFS
KEYWORD
nonn,mult
AUTHOR
N. J. A. Sloane, Dec 25 2009, following a suggestion from Jonathan Vos Post.
EXTENSIONS
More terms from R. J. Mathar, Jan 21 2010
STATUS
approved