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A234141 Numbers k such that triangular(k) - m is a triangular number (A000217), where m is the largest square less than triangular(k). 3
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 (list; graph; refs; listen; history; text; internal format)
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

Cf. A000217, A000290, A234142, A234143.

Sequence in context: A187479 A013947 A202342 * A093517 A248858 A145018

Adjacent sequences:  A234138 A234139 A234140 * A234142 A234143 A234144

KEYWORD

nonn

AUTHOR

Alex Ratushnyak, Dec 19 2013

STATUS

approved

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Last modified January 25 19:09 EST 2020. Contains 331249 sequences. (Running on oeis4.)