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%I #7 Mar 25 2017 20:41:55
%S 1,1,2,5,11,35,106,337,1112,3741,12821,44576,156862,557580,1999117,
%T 7221134,26253632,95996850,352798772,1302457652,4828002125,
%U 17962539164,67052864821,251066424023,942692613615,3548654963966,13390078255129,50635057984917
%N Number of n-element subsets of [2n] whose sum is a triangular number.
%H Alois P. Heinz, <a href="/A284251/b284251.txt">Table of n, a(n) for n = 0..100</a>
%F a(n) = A284249(2n,n).
%Y Cf. A281872, A284249.
%K nonn
%O 0,3
%A _Alois P. Heinz_, Mar 23 2017
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