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A170817 a(n) = product of distinct primes of form 4k+1 that divide n. 4

%I

%S 1,1,1,1,5,1,1,1,1,5,1,1,13,1,5,1,17,1,1,5,1,1,1,1,5,13,1,1,29,5,1,1,

%T 1,17,5,1,37,1,13,5,41,1,1,1,5,1,1,1,1,5,17,13,53,1,5,1,1,29,1,5,61,1,

%U 1,1,65,1,1,17,1,5,1,1,73,37,5,1,1,13,1,5,1,41,1,1,85,1,29,1

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

%H Harvey P. Dale, <a href="/A170817/b170817.txt">Table of n, a(n) for n = 1..1000</a>

%p a:= n-> mul (i, i=map (x-> x[1], select (x-> isprime (x[1]) and irem (x[1], 4)=1, ifactors(n)[2]))): seq (a(n), n=1..120);

%t Table[Times@@Select[Transpose[FactorInteger[n]][[1]],Mod[#,4]==1&], {n,90}] (* _Harvey P. Dale_, Dec 07 2012 *)

%Y Cf. A170818-A170819, A097706, A083025, A170824, A170825.

%K nonn,mult

%O 1,5

%A _N. J. A. Sloane_, Dec 22 2009

%E Corrected and extended with Maple program by _Alois P. Heinz_, Dec 23 2009

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Last modified May 6 00:41 EDT 2021. Contains 343579 sequences. (Running on oeis4.)