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 A125602 #27 Sep 08 2022 08:45:28
%S A125602 19,31,109,199,409,571,631,829,1489,1999,2341,2971,3529,4621,4789,
%T A125602 7039,7669,8779,9721,10459,10711,13681,14851,16069,16381,17659,20011,
%U A125602 20359,23251,25939,27541,29191,29611,31321,34429,36739,40099,40591,42589
%N A125602 Centered triangular numbers that are prime.
%C A125602 Prime terms in A005448, or primes of the form 3n(n-1)/2 + 1.
%C A125602 Primes that are the sum of 3 consecutive triangular numbers. - _Vicente Izquierdo Gomez_, Nov 03 2015
%H A125602 Vincenzo Librandi, <a href="/A125602/b125602.txt">Table of n, a(n) for n = 1..1000</a>
%p A125602 select(isprime, [seq(3*n*(n-1)/2+1, n=1..1000)]); # _Robert Israel_, Nov 03 2015
%t A125602 lst={};Do[If[PrimeQ[p=3n(n-1)/2+1], (*Print[p];*)AppendTo[lst, p]], {n, 10^3}];lst (* _Vladimir Joseph Stephan Orlovsky_, Aug 21 2008 *)
%t A125602 Select[Total/@Partition[Accumulate[Range[200]],3,1],PrimeQ] (* _Harvey P. Dale_, Dec 29 2020 *)
%o A125602 (Magma) [a: n in [0..200] | IsPrime(a) where a is (3*n^2 - 3*n + 2) div 2]; // _Vincenzo Librandi_, Mar 22 2013
%o A125602 (PARI) is(n)=n%6==1 && ispolygonal((n-1)/3,3) && isprime(n) \\ _Charles R Greathouse IV_, Nov 03 2015
%Y A125602 Cf. A005448, A125603.
%K A125602 nonn,easy
%O A125602 1,1
%A A125602 _Zak Seidov_, Nov 27 2006