A111074 Let t(n) denote the triangular numbers (A000217). Sequence mixes t(n+2) and t(n).

3, 0, 6, 1, 10, 3, 15, 6, 21, 10, 28, 15, 36, 21, 45, 28, 55, 36, 66, 45, 78, 55, 91, 66, 105, 78, 120, 91, 136, 105, 153, 120, 171, 136, 190, 153, 210, 171, 231, 190, 253, 210, 276, 231, 300, 253, 325, 276, 351, 300, 378, 325, 406, 351, 435, 378, 465, 406, 496, 435

Offset: 0

Author

Stuart M. Ellerstein (ellerstein(AT)aol.com), Oct 10 2005

Keywords

• easy
• nonn

Crossrefs

Cf. mix of t(n+1) and t(n): A008795.

Programs

Mathematica

Flatten[ Table[{(n + 2)(n + 3)/2, n(n + 1)/2}, {n, 0, 29}]] (* Robert G. Wilson v *)

Formula

G.f.: (3-3x+x^3)/((1-x)(1-x^2)^2); a(n)=a(n-1)+2a(n-2)-2a(n-3)-a(n-4)+a(n-5); - Paul Barry, Mar 22 2006

Extensions

More terms from Robert G. Wilson v, Oct 11 2005