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 A331399 #5 Jan 16 2020 13:19:40 %S A331399 2,3,5,29,59 %N A331399 Numbers k such that A000129(k) and A001333(k) are both prime. %C A331399 This sequence is the intersection of A096650 and A099088. %C A331399 The k-th square triangular number A001110(k) = (A000129(k)*A001333(k))^2 has exactly 9 divisors iff k is in this sequence, so if a(5) is the final term of this sequence, then there are only 5 triangular numbers that have exactly 9 divisors (cf. A331234). %Y A331399 Cf. A001110 (numbers that are both triangular and square), A000129 (Pell numbers), A001333 (numerators of continued fraction convergents to sqrt(2); equivalently, prime companion Pell numbers, divided by 2), A096650 (indices of prime Pell numbers), A099088 (indices of prime companion Pell numbers, divided by 2), A331234 (triangular numbers having exactly 9 divisors). %K A331399 nonn,more,hard %O A331399 1,1 %A A331399 _Jon E. Schoenfield_, Jan 16 2020