A320850 - OEIS

%I #4 Oct 22 2018 12:00:33

%S 1,1,3,6,11,20,32,48,70,98,132,174,226,287,359,444,542,655,783,928,

%T 1092,1275,1479,1707,1957,2231,2534,2865,3225,3617,4040,4497,4993,

%U 5527,6098,6710,7363,8062,8810,9605,10447,11342,12291,13295,14358,15478,16658,17904

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

%H Alois P. Heinz, <a href="/A320850/b320850.txt">Table of n, a(n) for n = 4..1000</a>

%Y Column k=4 of A284249.

%Y Cf. A000217.

%K nonn

%O 4,3

%A _Alois P. Heinz_, Oct 22 2018