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 A373591 #12 Jun 17 2024 07:11:17 %S A373591 0,0,0,0,0,0,1,0,0,0,0,0,1,1,0,0,0,0,1,0,1,0,0,0,0,1,0,1,0,0,1,0,0,0, %T A373591 1,0,1,1,1,0,0,1,1,0,0,0,0,0,2,0,0,1,0,0,0,1,1,0,0,0,1,1,1,0,1,0,1,0, %U A373591 0,1,0,0,1,1,0,1,1,1,1,0,0,0,0,1,0,1,0,0,0,0,2,0,1,0,1,0,1,2,0,0,0,0,1,1,1 %N A373591 Number of primes congruent to 1 modulo 3 dividing n (with multiplicity). %H A373591 Antti Karttunen, <a href="/A373591/b373591.txt">Table of n, a(n) for n = 1..100000</a> %F A373591 a(n) = A001222(A248909(n)). %F A373591 a(n) = A001222(n) - (A007949(n)+A373592(n)). %F A373591 Totally additive with a(3) = 0, a(p) = 1 if p == 1 (mod 3), and a(p) = 0 if p == 2 (mod 3). - _Amiram Eldar_, Jun 17 2024 %t A373591 f[p_, e_] := If[Mod[p, 3] == 1, e, 0]; f[3, e_] := 0; a[1] = 0; a[n_] := Plus @@ f @@@ FactorInteger[n]; Array[a, 100] (* _Amiram Eldar_, Jun 17 2024 *) %o A373591 (PARI) A373591(n) = sum(i=1, #n=factor(n)~, (1==n[1, i]%3)*n[2, i]); \\ After code in A083025 %Y A373591 Cf. A001222, A007949, A248909, A373592. %Y A373591 Cf. also A065339, A083025. %K A373591 nonn %O A373591 1,49 %A A373591 _Antti Karttunen_, Jun 13 2024