A078722 a(n) = prime(n*(n+1)/2+2).

3, 5, 11, 19, 37, 59, 83, 113, 163, 211, 269, 337, 409, 487, 587, 673, 787, 907, 1031, 1163, 1301, 1471, 1613, 1789, 1997, 2179, 2381, 2617, 2801, 3049, 3319, 3557, 3821, 4091, 4373, 4673, 4993, 5323, 5651, 5981, 6317, 6691, 7039, 7487, 7853, 8269, 8693, 9109

Offset: 0

Author

Cino Hilliard, Dec 20 2002

Keywords

• nonn
• easy

Comments

The sum of the reciprocals of the terms appears to converge.

Links

• Harvey P. Dale, Table of n, a(n) for n = 0..1000

Crossrefs

Cf. A000040.

Apart from initial term, primes in second diagonal of triangle in A078721.

Programs

Magma

[NthPrime(n*(n+1) div 2+2): n in [0..50]]; // Vincenzo Librandi, Jun 08 2016

Mathematica

Prime[Accumulate[Range[0,50]]+2] (* Harvey P. Dale, Aug 16 2014 *)

PARI

triprimes(n) = { sr = 0; for(j=0,n, x = j*(j+1)/2+2; z = prime(x); sr+=1.0/z; print1(z, ", "); ); print(); /* print(sr); */}