A265140 Numbers that are the sum of two distinct nonzero triangular numbers in exactly one way.

4, 7, 9, 11, 13, 18, 21, 22, 24, 25, 27, 29, 34, 36, 37, 38, 39, 42, 43, 48, 49, 55, 56, 57, 58, 60, 61, 64, 65, 66, 67, 69, 70, 72, 73, 79, 83, 84, 87, 88, 91, 92, 93, 97, 99, 100, 101, 102, 108, 112, 114, 115, 119, 120, 127, 130, 135, 136, 137, 139, 142, 144

Offset

1,1

Links

Table of n, a(n) for n=1..62.

Mathematica

r = 144; lst = Table[0, {r}]; lim = Floor[Sqrt[8*r - 7]]; Do[num = (i^2 + i)/2 + (j^2 + j)/2; If[num <= r, lst[[num]]++], {i, lim}, {j, i - 1}]; Flatten@Position[lst, 1]

Crossrefs

Cf. A000217, A051533, A260647, A262749 (more than one way), A265134 (exactly two ways), A265135 (more than two ways), A265136 (exactly three ways), A265137 (more than three ways), A265138 (exactly four ways).

Sequence in context: A260647 A310945 A310946 * A288510 A233473 A109180

Adjacent sequences: A265137 A265138 A265139 * A265141 A265142 A265143

Keyword

nonn

Author

Arkadiusz Wesolowski, Dec 02 2015

Status

approved