A320848 Number of 2-element subsets of [n] whose sum is a triangular number.

1, 1, 2, 3, 4, 5, 7, 9, 10, 12, 14, 16, 18, 20, 22, 24, 26, 29, 32, 34, 36, 39, 42, 45, 48, 51, 54, 57, 60, 63, 66, 69, 73, 77, 80, 83, 86, 89, 93, 97, 101, 105, 109, 112, 116, 120, 124, 128, 132, 136, 140, 145, 150, 154, 158, 162, 166, 170, 174, 179, 184, 189

Offset: 2

Author

Alois P. Heinz, Oct 22 2018

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 2..10000

Crossrefs

Column k=2 of A284249.

Cf. A000217.