A320855 - OEIS

%I #4 Oct 22 2018 12:03:18

%S 1,1,6,21,64,174,419,930,1921,3741,6933,12303,21044,34839,56044,87885,

%T 134682,202181,297873,431423,615166,864673,1199421,1643537,2226716,

%U 2985188,3962845,5212562,6797615,8793297,11288719,14388852,18216738,22915930,28653268

%N Number of 9-element subsets of [n] whose sum is a triangular number.

%H Alois P. Heinz, <a href="/A320855/b320855.txt">Table of n, a(n) for n = 9..1000</a>

%Y Column k=9 of A284249.

%Y Cf. A000217.

%K nonn

%O 9,3

%A _Alois P. Heinz_, Oct 22 2018