OFFSET
0,7
LINKS
Eric Weisstein's World of Mathematics, Square Pyramidal Number
EXAMPLE
a(20) = 6 because we have [14, 5, 1], [14, 1, 5], [5, 14, 1], [5, 1, 14], [1, 14, 5] and [1, 5, 14].
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 03 2020
STATUS
approved