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

4,3

Links

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

Crossrefs

Column k=4 of A284249.

Cf. A000217.

Sequence in context: A262987 A191696 A252479 * A180086 A116365 A297443

Adjacent sequences: A320847 A320848 A320849 * A320851 A320852 A320853

Keyword

nonn

Author

Alois P. Heinz, Oct 22 2018

Status

approved