OFFSET
1,2
COMMENTS
The sequence of triangular(a(n)) begins: 1, 3, 6, 10, 15, 66, 78, 120, 190, 210, 253, 325, ...
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[215], IntegerQ@Sqrt[8 ((Floor@Sqrt[(#^2 + #)/2] + 1)^2 - (#^2 + #)/2) + 1] &] (* Ivan Neretin, May 29 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Dec 19 2013
STATUS
approved