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 A226070 #16 Aug 29 2025 11:02:52 %S A226070 1,2,4,134,2174,154634 %N A226070 Numbers k such that k^2-1 is a triangular number and k^2+1 is a prime. %C A226070 Subsequence of A006452 that consists of the terms k such that k^2+1 is prime. %C A226070 a(7) is too large to include here (see b-file). - _Max Alekseyev_, Jan 30 2014 %H A226070 Max Alekseyev, <a href="/A226070/b226070.txt">Table of n, a(n) for n = 1..12</a> %t A226070 Select[Range[155000],PrimeQ[#^2+1]&&OddQ[Sqrt[8(#^2-1)+1]]&] (* _Harvey P. Dale_, Jul 19 2019 *) %o A226070 (C) // see A226069. %Y A226070 Corresponding primes: A226069. %Y A226070 Indices of corresponding triangular numbers: A226071. %Y A226070 Cf. A226072-A226074. %K A226070 nonn,changed %O A226070 1,2 %A A226070 _Alex Ratushnyak_, May 25 2013 %E A226070 Terms a(7)-a(12) from _Max Alekseyev_, Jan 30 2014