OFFSET
0,4
LINKS
Eric Weisstein's World of Mathematics, Triangular Number
EXAMPLE
[1]
[1 1] [1]
[1 1 1] [1 1] [1]
a(10) = 4 because we have [1 1 1 1], [1 3 3], [3 6] and [10].
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Dec 05 2020
STATUS
approved