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 A324967 #21 Oct 06 2023 04:55:51
%S A324967 0,0,1,0,0,1,1,0,1,0,0,1,1,1,1,0,0,1,1,0,2,0,0,1,0,1,1,1,1,1,0,0,1,0,
%T A324967 1,1,1,1,2,0,0,2,1,0,1,0,0,1,1,0,1,1,1,1,0,1,2,1,0,1,1,0,2,0,1,1,0,0,
%U A324967 1,1,1,1,0,1,1,1,1,2,1,0,1,0,0,2,0,1,2
%N A324967 Number of distinct even prime indices of n.
%C A324967 A prime index of n is a number m such that prime(m) divides n. The multiset of prime indices of n is row n of A112798.
%C A324967 If x and y are coprime then a(x*y) = a(x) + a(y). - _Robert Israel_, Mar 24 2019
%H A324967 Robert Israel, <a href="/A324967/b324967.txt">Table of n, a(n) for n = 1..10000</a>
%F A324967 a(n) = A001221(n) - A324966(n). - _Robert Israel_, Mar 24 2019
%F A324967 G.f.: Sum_{k>=1} x^prime(2*k) / (1 - x^prime(2*k)). - _Ilya Gutkovskiy_, Feb 12 2020
%F A324967 Additive with a(p^e) = 1 if primepi(p) is even and 0 otherwise. - _Amiram Eldar_, Oct 06 2023
%e A324967 180180 has prime indices {1,1,2,2,3,4,5,6}, so a(180180) = 3.
%p A324967 f:= proc(n) nops(select(type,map(numtheory:-pi,numtheory:-factorset(n)),even)) end proc:
%p A324967 map(f, [$1..100]); # _Robert Israel_, Mar 24 2019
%t A324967 Table[Count[If[n==1,{},FactorInteger[n]],{_?(EvenQ[PrimePi[#]]&),_}],{n,100}]
%o A324967 (PARI) a(n) = my(f=factor(n)[,1]); sum(k=1, #f, !(primepi(f[k]) % 2)); \\ _Michel Marcus_, Mar 22 2019
%Y A324967 Cf. A000720, A001221, A003963, A005087, A066208, A112798, A257991, A257992, A289509, A324929, A324966.
%K A324967 nonn,easy
%O A324967 1,21
%A A324967 _Gus Wiseman_, Mar 21 2019