A234142 Numbers k such that m - triangular(k) is a triangular number (A000217), where m is the least square above triangular(k).

1, 2, 3, 4, 5, 11, 12, 15, 19, 20, 22, 25, 26, 29, 32, 33, 36, 40, 43, 47, 50, 52, 54, 57, 61, 64, 68, 70, 71, 73, 75, 78, 82, 85, 89, 90, 92, 96, 99, 103, 106, 110, 113, 114, 117, 120, 121, 122, 124, 127, 131, 134, 135, 141, 148, 152, 155, 172, 173, 188, 189, 196, 213

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

Cf. A000217, A000290, A234141, A234143.

Sequence in context: A069908 A130640 A214653 * A116068 A104420 A188532

Adjacent sequences: A234139 A234140 A234141 * A234143 A234144 A234145

Keyword

nonn

Author

Alex Ratushnyak, Dec 19 2013

Status

approved