A226070 - OEIS

%I #12 May 13 2023 19:12:32

%S 1,2,4,134,2174,154634

%N Numbers n such that n^2-1 is a triangular number and n^2+1 is a prime.

%C Subsequence of A006452 that consists of the terms n such that n^2+1 is prime.

%C a(7) is too large to include here (see b-file). - _Max Alekseyev_, Jan 30 2014

%H Max Alekseyev, <a href="/A226070/b226070.txt">Table of n, a(n) for n = 1..12</a>

%t Select[Range[155000],PrimeQ[#^2+1]&&OddQ[Sqrt[8(#^2-1)+1]]&] (* _Harvey P. Dale_, Jul 19 2019 *)

%o (C) // see A226069.

%Y Corresponding primes: A226069.

%Y Indices of corresponding triangular numbers: A226071.

%Y Cf. A226072-A226074.

%K nonn

%O 1,2

%A _Alex Ratushnyak_, May 25 2013

%E Terms a(7)-a(12) from _Max Alekseyev_, Jan 30 2014