A320850 Number of 4-element subsets of [n] whose sum is a triangular number.

1, 1, 3, 6, 11, 20, 32, 48, 70, 98, 132, 174, 226, 287, 359, 444, 542, 655, 783, 928, 1092, 1275, 1479, 1707, 1957, 2231, 2534, 2865, 3225, 3617, 4040, 4497, 4993, 5527, 6098, 6710, 7363, 8062, 8810, 9605, 10447, 11342, 12291, 13295, 14358, 15478, 16658, 17904

Offset: 4

Author

Alois P. Heinz, Oct 22 2018

Keywords

• nonn

Links

• Alois P. Heinz, Table of n, a(n) for n = 4..1000

Crossrefs

Column k=4 of A284249.

Cf. A000217.