A116010 n+prime(n)+prime(prime(n)) is a triangular number, where prime(n) is the n-th prime.

1, 2, 4, 210, 381, 573, 1009, 1094, 1117, 2139, 3123, 4471, 6459, 7197, 12534, 13177, 13335, 13603, 14178, 19479, 21512, 23427, 31833, 35965, 37924, 38446, 39726, 55375, 58851, 59232, 61015, 63849, 64344, 70471, 75616, 76770, 79590

Offset

1,2

Links

Harvey P. Dale, Table of n, a(n) for n = 1..145

Example

1009+prime(1009)+prime(prime(1009))=T(426).

Mathematica

Select[Range[80000], OddQ[Sqrt[1+8(#+Prime[#]+Prime[Prime[#]])]]&] (* Harvey P. Dale, Aug 11 2019 *)

Prog

(PARI) isok(n) = ispolygonal(n + prime(n) + prime(prime(n)), 3); \\ Michel Marcus, Jan 27 2014

Crossrefs

Cf. A116011.

Sequence in context: A009796 A018651 A068479 * A018677 A173637 A111355

Adjacent sequences: A116007 A116008 A116009 * A116011 A116012 A116013

Keyword

nonn

Author

Giovanni Resta, Feb 13 2006

Status

approved