OFFSET
1,2
LINKS
Eric Weisstein's World of Mathematics, Pentagonal Number
EXAMPLE
Let S(k, m) denote the sum of m pentagonal numbers starting from the k-th. We have
a(1) = S(1, 1);
a(2) = S(14, 1) = S(2, 7);
a(3) = S(103, 24) = S(19, 80) = S(67, 41);
a(4) = S(10833, 484) = S(4542, 1936) = S(9153, 660) = S(2817, 3036);
CROSSREFS
KEYWORD
nonn,hard,more
AUTHOR
Ilya Gutkovskiy, Apr 12 2020
EXTENSIONS
a(4) from Giovanni Resta, Apr 13 2020
STATUS
approved