OFFSET
0,10
LINKS
Eric Weisstein's World of Mathematics, Octagonal Number
EXAMPLE
a(30) = 6 because we have [21, 8, 1], [21, 1, 8], [8, 21, 1], [8, 1, 21], [1, 21, 8] and [1, 8, 21].
CROSSREFS
KEYWORD
nonn
AUTHOR
Ilya Gutkovskiy, Feb 04 2020
STATUS
approved