A115882 Numbers k such that k + prime(k) gives a triangular number.
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
Keywords
Examples
103 + prime(103) = 103 + 563 = 666 = T(36).
Links
- T. D. Noe, Table of n, a(n) for n = 1..1000
Programs
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Mathematica
TriangularQ[n_] := IntegerQ[Sqrt[1 + 8*n]]; Select[Range[20000], TriangularQ[# + Prime[#]] &] (* T. D. Noe, Jan 27 2014 *)
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PARI
isok(n) = ispolygonal(n + prime(n), 3); \\ Michel Marcus, Jan 25 2014