A364799 - OEIS

A364799

Triangular numbers that for some k >= 1 are also the sum of the first k odd primes.

3, 15, 1236378, 1454365, 3541791, 104856921, 2677839153, 3656187921870, 3973810409128, 1448587865213374600, 36691639282445615088081

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OFFSET

1,1

COMMENTS

a(n) = A000217(i) = A071148(j) for appropriate i, j.

LINKS

EXAMPLE

15 is a term because 15 = 1 + 2 + 3 + 4 + 5 = 3 + 5 + 7.

MATHEMATICA

Select[Accumulate[Prime[Range[2, 1000000]]], IntegerQ[Sqrt[8 # + 1]] &]

PROG

(PARI) lista(nn) = my(s=0); forprime(p=3, nn, s+=p; if(ispolygonal(s, 3), print1(s, ", "))) \\ Jinyuan Wang, Aug 10 2023

CROSSREFS

Intersection of A000217 and A071148.

KEYWORD

nonn,more

AUTHOR

EXTENSIONS

a(10) from Jinyuan Wang, Aug 10 2023

a(11) from Martin Ehrenstein, Aug 23 2023

STATUS

approved