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A234142
Numbers k such that m - triangular(k) is a triangular number (A000217), where m is the least square above triangular(k).
3
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
MATHEMATICA
Select[Range[215], IntegerQ@Sqrt[8 ((Floor@Sqrt[(#^2 + #)/2] + 1)^2 - (#^2 + #)/2) + 1] &] (* Ivan Neretin, May 29 2016 *)
CROSSREFS
KEYWORD
nonn
AUTHOR
Alex Ratushnyak, Dec 19 2013
STATUS
approved