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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
OFFSET
1,2
COMMENTS
The sequence of triangular(a(n)) begins: 1, 10, 15, 28, 55, 91, 136, 190, 231, 253, 325, ...
LINKS
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