A234141 Numbers k such that triangular(k) - m is a triangular number (A000217), where m is the largest square less than triangular(k).

1, 4, 5, 7, 10, 13, 16, 19, 21, 22, 25, 28, 40, 42, 59, 60, 64, 76, 85, 89, 93, 109, 110, 124, 127, 142, 144, 148, 161, 165, 178, 184, 195, 212, 229, 233, 246, 247, 263, 265, 268, 280, 297, 313, 314, 331, 346, 348, 349, 365, 373, 376, 382, 399, 416, 433, 445, 450

Offset: 1

Author

Alex Ratushnyak, Dec 19 2013

Keywords

• nonn

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

Crossrefs

Cf. A000217, A000290, A234142, A234143.

Programs

Mathematica

Select[Range[450], IntegerQ@Sqrt[8 ((#^2 + #)/2 - (Ceiling@Sqrt[(#^2 + #)/2] - 1)^2) + 1] &] (* Ivan Neretin, May 29 2016 *)