A008912 Truncated triangular numbers (of form n*(n-3)/2 - k^2+k*n+1 for 1<=k<n).

1, 3, 6, 7, 10, 12, 15, 18, 19, 21, 25, 27, 28, 33, 36, 37, 42, 45, 46, 48, 52, 55, 57, 60, 61, 63, 66, 69, 73, 75, 78, 82, 87, 88, 90, 91, 96, 102, 105, 106, 108, 111, 117, 118, 120, 123, 126, 127, 133, 135, 136, 141, 144, 145, 147, 150, 153, 160, 162, 165

Offset

1,2

Links

Table of n, a(n) for n=1..60.

J. H. Conway and N. J. A. Sloane, Low-Dimensional Lattices VII: Coordination Sequences, Proc. Royal Soc. London, A453 (1997), 2369-2389 (pdf).

Formula

Numbers of the form (n^2+n+k^2-k+4kn)/2, n>=1, k>=0. - Bob Selcoe, Nov 14 2018

Crossrefs

Cf. A008867.

Sequence in context: A184903 A330180 A330184 * A101885 A096068 A045412

Adjacent sequences: A008909 A008910 A008911 * A008913 A008914 A008915

Keyword

nonn

Author

N. J. A. Sloane, R. K. Guy

Status

approved