A322422 Numbers k such that the sum of the first k*(k+1) primes is prime.

1, 2, 3, 11, 18, 31, 34, 49, 57, 76, 79, 84, 97, 118, 139, 140, 172, 175, 183, 184, 185, 191, 208, 218, 221, 232, 233, 247, 262, 266, 294, 313, 315, 323, 333, 334, 339, 344, 351, 361, 366, 372, 407, 413, 436, 445, 461, 473, 478, 500, 545, 546, 556, 564, 577

Offset: 1

Author

Ray Chandler, Dec 07 2018

Keywords

• nonn

Links

• Ray Chandler, Table of n, a(n) for n = 1..1000

Crossrefs

Cf. A002378, A007504, A322420, A322421.

Programs

Mathematica

f[n_] := Sum[Prime[k], {k, n}]; Select[Range[500],
PrimeQ[f[#*(# + 1)]] &]

Formula

A322421(n) = A322420(a(n)) = A007504(A002378(a(n))).