A225115 Triangular numbers of the form p^k - 1, where p is a prime number and k >= 2.

3, 15, 120, 528, 4095, 139128, 160554240, 812293020528, 379188080252621270252095320

Offset: 1

Author

Alex Ratushnyak, Apr 29 2013

Keywords

• nonn
• hard
• more

Comments

There are at least other 4 terms greater than a(9) that can be easily obtained by solving the Diophantine equation T(n) = p^2-1, the smallest being T(75055187665070250755513356704300447). - Giovanni Resta, Apr 29 2013

Crossrefs

Cf. A006454, A025475.

Programs

PARI

t=0;for(n=1,10^9,t+=n; if(isprimepower(t+1)>=2,print1(t,", "))); \\ Joerg Arndt, Apr 29 2013

Extensions

a(9) from Giovanni Resta, Apr 29 2013