login
The OEIS Foundation is supported by donations from users of the OEIS and by a grant from the Simons Foundation.

 

Logo


Hints
(Greetings from The On-Line Encyclopedia of Integer Sequences!)
A170824 a(n) = product of distinct primes of form 6k+1 that divide n. 4
1, 1, 1, 1, 1, 1, 7, 1, 1, 1, 1, 1, 13, 7, 1, 1, 1, 1, 19, 1, 7, 1, 1, 1, 1, 13, 1, 7, 1, 1, 31, 1, 1, 1, 7, 1, 37, 19, 13, 1, 1, 7, 43, 1, 1, 1, 1, 1, 7, 1, 1, 13, 1, 1, 1, 7, 19, 1, 1, 1, 61, 31, 7, 1, 13, 1, 67, 1, 1, 7, 1, 1, 73, 37, 1, 19, 7, 13, 79, 1, 1, 1, 1, 7, 1, 43, 1, 1, 1, 1, 91, 1, 31, 1 (list; graph; refs; listen; history; text; internal format)
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

Cf. A002476, A170817.

Cf. A140213. [R. J. Mathar, Jan 21 2010]

Differs from A248909 for the first time at n=49, where a(49) = 7, while A248909(49) = 49.

Sequence in context: A339748 A325470 A240831 * A248909 A140213 A331927

Adjacent sequences:  A170821 A170822 A170823 * A170825 A170826 A170827

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

Lookup | Welcome | Wiki | Register | Music | Plot 2 | Demos | Index | Browse | More | WebCam
Contribute new seq. or comment | Format | Style Sheet | Transforms | Superseeker | Recent
The OEIS Community | Maintained by The OEIS Foundation Inc.

License Agreements, Terms of Use, Privacy Policy. .

Last modified May 5 18:20 EDT 2021. Contains 343572 sequences. (Running on oeis4.)