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A170824
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a(n) = product of distinct primes of form 6k+1 that divide n.
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4
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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
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OFFSET
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1,7
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LINKS
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FORMULA
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MAPLE
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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:
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MATHEMATICA
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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 *)
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PROG
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(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
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CROSSREFS
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Differs from A248909 for the first time at n=49, where a(49) = 7, while A248909(49) = 49.
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KEYWORD
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nonn,mult
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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