OFFSET
1,2
COMMENTS
The sequence of triangular(a(n)) begins: 1, 10, 15, 28, 55, 91, 136, 190, 231, 253, 325, ...
LINKS
Ivan Neretin, Table of n, a(n) for n = 1..10000
MATHEMATICA
Select[Range[450], IntegerQ@Sqrt[8 ((#^2 + #)/2 - (Ceiling@Sqrt[(#^2 + #)/2] - 1)^2) + 1] &] (* Ivan Neretin, May 29 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Dec 19 2013
STATUS
approved