A364696 Nonnegative integers k such that the sum of the first k primes is a pentagonal number.

0, 2, 77, 24587, 48070640, 471412484, 7471587112

Offset

1,2

Links

Table of n, a(n) for n=1..7.

Wikipedia, Pentagonal number.

Index to sequences related to polygonal numbers

Example

2 is a term because the sum of the first 2 primes (2 + 3 = 5) is a pentagonal number.

Mathematica

A364696list[kmax_]:=Module[{p=0}, Join[{0}, Table[If[IntegerQ[(Sqrt[24(p+=Prime[k])+1]+1)/6], k, Nothing], {k, kmax}]]]; A364696list[25000] (* Paolo Xausa, Oct 06 2023 *)

Crossrefs

Cf. A000326, A007504, A033997, A175133, A364691, A364695, A366270.

Sequence in context: A048358 A124456 A338588 * A308373 A183578 A184965

Adjacent sequences: A364693 A364694 A364695 * A364697 A364698 A364699

Keyword

nonn,hard,more

Author

Paolo Xausa, Aug 03 2023

Extensions

a(5) from Michel Marcus, Aug 04 2023

a(6)-a(7) from Hugo Pfoertner, Aug 04 2023

Status

approved