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%I #15 Nov 14 2018 15:49:52
%S 1,3,6,7,10,12,15,18,19,21,25,27,28,33,36,37,42,45,46,48,52,55,57,60,
%T 61,63,66,69,73,75,78,82,87,88,90,91,96,102,105,106,108,111,117,118,
%U 120,123,126,127,133,135,136,141,144,145,147,150,153,160,162,165
%N Truncated triangular numbers (of form n*(n-3)/2 - k^2+k*n+1 for 1<=k<n).
%H J. H. Conway and N. J. A. Sloane, Low-Dimensional Lattices VII: Coordination Sequences, Proc. Royal Soc. London, A453 (1997), 2369-2389 (<a href="http://neilsloane.com/doc/Me220.pdf">pdf</a>).
%F Numbers of the form (n^2+n+k^2-k+4kn)/2, n>=1, k>=0. - _Bob Selcoe_, Nov 14 2018
%Y Cf. A008867.
%K nonn
%O 1,2
%A _N. J. A. Sloane_, _R. K. Guy_
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