This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A170817 #12 Jun 09 2025 09:03:12
%S A170817 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 A170817 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 A170817 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 A170817 a(n) = product of distinct primes of form 4k+1 that divide n.
%H A170817 Harvey P. Dale, <a href="/A170817/b170817.txt">Table of n, a(n) for n = 1..1000</a>
%p A170817 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 A170817 Table[Times@@Select[Transpose[FactorInteger[n]][[1]],Mod[#,4]==1&], {n,90}] (* _Harvey P. Dale_, Dec 07 2012 *)
%o A170817 (PARI) a(n) = {my(f = factor(n)); prod(i = 1, #f~, if(f[i,1] % 4 == 1, f[i,1], 1));} \\ _Amiram Eldar_, Jun 09 2025
%Y A170817 Cf. A170818, A170819, A097706, A083025, A170824, A170825.
%K A170817 nonn,mult,easy
%O A170817 1,5
%A A170817 _N. J. A. Sloane_, Dec 22 2009
%E A170817 Corrected and extended with Maple program by _Alois P. Heinz_, Dec 23 2009