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A322239 a(n) = [x^n*y^n] 1/(1 - x - y - x^2 + x*y - y^2). 1
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 (list; graph; refs; listen; history; text; internal format)
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 A271425 A267081

Adjacent sequences:  A322236 A322237 A322238 * A322240 A322241 A322242

KEYWORD

nonn

AUTHOR

Paul D. Hanna, Dec 12 2018

STATUS

approved

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Last modified August 11 19:16 EDT 2020. Contains 336428 sequences. (Running on oeis4.)