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 A133363 #15 Mar 17 2025 22:23:18
%S A133363 3,4,8,11,16,19,20,23,31,36,39,44,48,55,56,68,71,76,80,83,84,95,99,
%T A133363 103,104,108,115,116,124,131,135,139,140,144,151,156,163,164,168,171,
%U A133363 180,184,188,191,195,203,204,215,216,219,220,223,244,256,263,268,271,276
%N A133363 Numbers m such that 1 + Sum_{k=1..m} 3*k is prime.
%C A133363 It appears that the first differences of this sequence are never of the form 4k+2.
%C A133363 This is true, because all terms == 0 or 3 (mod 4). - _Robert Israel_, Mar 16 2025
%H A133363 Robert Israel, <a href="/A133363/b133363.txt">Table of n, a(n) for n = 1..10000</a>
%p A133363 filter:= n -> isprime((3*n^2 + 3*n + 2)/2):
%p A133363 select(filter, [$1..1000]); # _Robert Israel_, Mar 16 2025
%t A133363 Select[Range[276],PrimeQ[1+Sum[3k,{k,#}]]&] (* _James C. McMahon_, Mar 15 2025 *)
%o A133363 (PARI) lista(nn) = select(n->(isprime(1+sum(k=1,n,3*k))), vector(nn, i, i)); \\ _Michel Marcus_, Jul 10 2014
%Y A133363 Cf. A067196, A134460.
%K A133363 nonn
%O A133363 1,1
%A A133363 _John W. Layman_, Oct 26 2007