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 A359380 #18 Jul 10 2024 16:48:13
%S A359380 1,4,5,7,8,11,13,16,17,19,20,23,25,28,29,31,32,35,37,40,41,43,44,47,
%T A359380 49,52,53,55,56,59,61,64,65,67,68,71,73,76,77,79,80,83,85,88,89,91,92,
%U A359380 95,97,100,101,103,104,107,109,112,113,115,116,119,121,124,125,127,128,131,133,136,137,139,140
%N A359380 Numbers that are neither multiples of 3 nor of the form 4u+2.
%C A359380 Numbers that are congruent to {1, 4, 5, 7, 8, 11} mod 12. - _Amiram Eldar_, Jan 24 2023
%H A359380 Amiram Eldar, <a href="/A359380/b359380.txt">Table of n, a(n) for n = 1..10000</a>
%H A359380 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1,-1,2,-1).
%F A359380 Sum_{n>=1} (-1)^(n+1)/a(n) = (1-1/(4*sqrt(3)))*Pi/3. - _Amiram Eldar_, Jan 24 2023
%F A359380 From _Stefano Spezia_, Jul 10 2024: (Start)
%F A359380 G.f.: x*(1 + 2*x - 2*x^2 + 2*x^3 + x^4)/((1 - x)^2*(1 + x^3)).
%F A359380 a(n) = (6*n - 3 - A057079(n+1) + 2*A010892(n+2)/3)/3 for n > 0. (End)
%t A359380 Select[Range[140], Mod[#, 3] > 0 && Mod[#, 4] != 2 &] (* _Amiram Eldar_, Dec 31 2022 *)
%o A359380 (PARI) isA359380(n) = A187074(n);
%Y A359380 Cf. A187074 (characteristic function).
%Y A359380 Cf. also A359375.
%Y A359380 Cf. A010892, A057079.
%K A359380 nonn,easy
%O A359380 1,2
%A A359380 _Antti Karttunen_, Dec 31 2022