A226070 Numbers k such that k^2-1 is a triangular number and k^2+1 is a prime.

1, 2, 4, 134, 2174, 154634

Offset: 1

Author

Alex Ratushnyak, May 25 2013

Keywords

• nonn
• changed

Comments

Subsequence of A006452 that consists of the terms k such that k^2+1 is prime.

a(7) is too large to include here (see b-file). - Max Alekseyev, Jan 30 2014

Links

• Max Alekseyev, Table of n, a(n) for n = 1..12

Crossrefs

Corresponding primes: A226069.

Indices of corresponding triangular numbers: A226071.

Cf. A226072-A226074.

Programs

C

// see A226069.

Mathematica

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

Extensions

Terms a(7)-a(12) from Max Alekseyev, Jan 30 2014