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A170825 a(n) is the product of the distinct primes of form 6*k-1 that divide n. 4
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 (list; graph; refs; listen; history; text; internal format)
OFFSET
1,5
LINKS
FORMULA
a(n) = A007947(A343431(n)) = A343431(A007947(n)). - Peter Munn, Jan 15 2022
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 *)
PROG
(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
CROSSREFS
Cf. A140214. - R. J. Mathar, Jan 21 2010
Sequence in context: A170817 A170818 A046622 * A140214 A343431 A366374
KEYWORD
nonn,mult,easy
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

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Last modified March 28 18:04 EDT 2024. Contains 371254 sequences. (Running on oeis4.)