OFFSET
1,1
COMMENTS
EXAMPLE
k=3 is a term: 2+3+5=10, and 10=4*5/2 is a triangular number, j=4.
k=5 is a term: 2+3+5+7+11=28, and 28=7*8/2 is a triangular number, j=7.
k=217 is a term: 2+3+...+1327=133386, and 133386=516*517/2 is a triangular number, j=516.
PROG
(PARI) isok(n) = ispolygonal(sum(k=1, n, prime(k)), 3); \\ Michel Marcus, Oct 13 2018
CROSSREFS
KEYWORD
nonn,more
AUTHOR
Ctibor O. Zizka, Feb 20 2010
EXTENSIONS
a(6)-a(10) from Nathaniel Johnston, May 10 2011 (a(7)-a(10) based on comments by Donovan Johnson)
Name, comment and example clarified by Ilya Gutkovskiy, Aug 07 2023
STATUS
approved