A322239 a(n) = [x^n*y^n] 1/(1 - x - y - x^2 + x*y - y^2).

1, 1, 9, 35, 199, 1005, 5475, 29469, 161685, 889759, 4932641, 27453471, 153432241, 860203135, 4836370101, 27257082723, 153943314903, 871064225325, 4936953721755, 28022734759125, 159272314734843, 906343638290133, 5163219745287591, 29442990216677985, 168050775902585751, 959985125666243145, 5488145767630988595, 31397773111113948245, 179747041781229841375

Offset

0,3

Comments

Central terms of triangle A123603.

Links

Table of n, a(n) for n=0..28.

Example

Triangle A123603 of coefficients of x^(n-k)*y^k in 1/(1 - x - y - x^2 + x*y - y^2), for n >= 0 and k = 0..n, begins
1;
1, 1;
2, 1, 2;
3, 3, 3, 3;
5, 5, 9, 5, 5;
8, 10, 17, 17, 10, 8;
13, 18, 36, 35, 36, 18, 13;
21, 33, 69, 81, 81, 69, 33, 21;
34, 59, 133, 167, 199, 167, 133, 59, 34;
55, 105, 249, 345, 435, 435, 345, 249, 105, 55;
89, 185, 462, 687, 945, 1005, 945, 687, 462, 185, 89; ...
in which the central terms form this sequence.

Prog

(PARI) {a(n) = polcoeff( polcoeff( 1/(1 - x - y - x^2 + x*y - y^2 +x*O(x^n) +y*O(y^n)), n, x), n, y)}
for(n=0, 30, print1(a(n), ", "))

Crossrefs

Cf. A123603, A192364.

Sequence in context: A002418 A118414 A279218 * A232282 A364573 A271425

Adjacent sequences: A322236 A322237 A322238 * A322240 A322241 A322242

Keyword

nonn

Author

Paul D. Hanna, Dec 12 2018

Status

approved