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A115882
Numbers k such that k + prime(k) gives a triangular number.
6
1, 20, 49, 65, 103, 176, 279, 284, 299, 437, 513, 553, 656, 973, 1271, 1779, 1921, 2156, 2312, 2347, 2554, 2759, 3176, 3379, 4008, 4028, 4132, 5255, 6354, 6764, 7116, 8299, 8334, 8366, 8723, 9277, 9755, 10092, 10475, 10631, 11429, 11842, 12633, 13157, 13627
OFFSET
1,2
EXAMPLE
103 + prime(103) = 103 + 563 = 666 = T(36).
MATHEMATICA
TriangularQ[n_] := IntegerQ[Sqrt[1 + 8*n]]; Select[Range[20000], TriangularQ[# + Prime[#]] &] (* T. D. Noe, Jan 27 2014 *)
PROG
(PARI) isok(n) = ispolygonal(n + prime(n), 3); \\ Michel Marcus, Jan 25 2014
CROSSREFS
KEYWORD
nonn
AUTHOR
Giovanni Resta, Feb 06 2006
STATUS
approved