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A170819 a(n) = product of distinct primes of the form 4k-1 that divide n. 5

%I

%S 1,1,3,1,1,3,7,1,3,1,11,3,1,7,3,1,1,3,19,1,21,11,23,3,1,1,3,7,1,3,31,

%T 1,33,1,7,3,1,19,3,1,1,21,43,11,3,23,47,3,7,1,3,1,1,3,11,7,57,1,59,3,

%U 1,31,21,1,1,33,67,1,69,7,71,3,1,1,3,19,77,3,79,1,3,1,83,21,1

%N a(n) = product of distinct primes of the form 4k-1 that divide n.

%C Multiplicative with a(p^e) = p*A011765(p+1), e > 0. - R. J. Mathar, Jun 07 2011

%H Michael De Vlieger, <a href="/A170819/b170819.txt">Table of n, a(n) for n = 1..10000</a>

%p A170819 := proc(n) a := 1 ; for p in numtheory[factorset](n) do if p mod 4 = 3 then a := a*p ; end if; end do: a ; end proc:

%p seq(A170819(n),n=1..20) ; # _R. J. Mathar_, Jun 07 2011

%t Array[Times @@ Select[FactorInteger[#][[All, 1]], Mod[#, 4] == 3 &] &, 85] (* _Michael De Vlieger_, Feb 19 2019 *)

%o (PARI) for(n=1,99, t=select(x->x%4==3, factor(n)[,1]); print1(prod(i=1,#t,t[i])","))

%Y Cf. A170817-A170818, A097706, A083025, A007947.

%K nonn,mult

%O 1,3

%A _N. J. A. Sloane_, Dec 23 2009

%E Extended with PARI program by _M. F. Hasler_, Dec 23 2009

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Last modified May 18 07:26 EDT 2021. Contains 343995 sequences. (Running on oeis4.)