A239093 Irregular triangle of incomplete tribonacci numbers t_n(s) (n >= 1, 0 <= s <= floor((n-1)/2)), read by rows.

1, 1, 1, 2, 1, 4, 1, 6, 7, 1, 8, 13, 1, 10, 23, 24, 1, 12, 37, 44, 1, 14, 55, 80, 81, 1, 16, 77, 140, 149, 1, 18, 103, 232, 273, 274, 1, 20, 133, 364, 493, 504, 1, 22, 167, 544, 865, 926, 927, 1, 24, 205, 780, 1461, 1692, 1705, 1, 26, 247, 1080, 2369, 3050, 3135, 3136, 1, 28, 293, 1452, 3693, 5376, 5753, 5768

Offset

1,4

Links

Table of n, a(n) for n=1..72.

J. L. Ramirez and V. F. Sirvent, Incomplete Tribonacci Numbers and Polynomials, Journal of Integer Sequences, Vol. 17, 2014, #14.4.2.

Formula

t_{n+3}(s+1) = t_{n+2}(s+1) + t_{n+1}(s) + t_n(s).

The third column is (essentially) 2m^2+5.

Example

Triangle begins:
1,
1,
1,2,
1,4,
1,6,7,
1,8,13,
1,10,23,24,
1,12,37,44,
1,14,55,80,81,
1,16,77,140,149,
1,18,103,232,273,274,
1,20,133,364,493,504,
...

Crossrefs

Sequence in context: A128099 A182242 A261605 * A263453 A108952 A088522

Adjacent sequences: A239090 A239091 A239092 * A239094 A239095 A239096

Keyword

nonn,tabf

Author

N. J. A. Sloane, Mar 23 2014

Status

approved