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 A171569 #6 Mar 15 2023 11:02:12
%S A171569 15,21,45,55,91,105,153,231,253,351,435,465,595,703,741,861,1035,1225,
%T A171569 1431,1485,1711,1891,1953,2145,2701,3003,3081,3321,3741,4005,4095,
%U A171569 4465,4753,5565,5671,6555,7021,7875,8515,9045,10011,10153,10731,11175,11781
%N A171569 Triangular numbers T such that T-2 is a prime.
%e A171569 15-2 = 13, 21-2 = 19, 45-2 = 43, ...
%t A171569 Select[s=0;Table[n*(n+1)/2,{n,6!}],PrimeQ[ #-2]&]
%t A171569 Select[Accumulate[Range[200]],PrimeQ[#-2]&] (* _Harvey P. Dale_, Apr 09 2018 *)
%Y A171569 Cf. A000217, A129545, A129752.
%K A171569 nonn
%O A171569 1,1
%A A171569 _Vladimir Joseph Stephan Orlovsky_, Dec 11 2009