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A054963 Number of cells in the first column of all directed column-convex polyominoes of area n+1. 1
1, 3, 9, 26, 72, 194, 515, 1357, 3563, 9340, 24466, 64068, 167749, 439191, 1149837, 3010334, 7881180, 20633222, 54018503, 141422305, 370248431, 969323008, 2537720614, 6643838856, 17393795977, 45537549099, 119218851345 (list; graph; refs; listen; history; text; internal format)
OFFSET

0,2

LINKS

Table of n, a(n) for n=0..26.

E. Barcucci, R. Pinzani and R. Sprugnoli, Directed column-convex polyominoes by recurrence relations, Lecture Notes in Computer Science, No. 668, Springer, Berlin (1993), pp. 282-298.

FORMULA

a(n) = fibonacci(2n)+fibonacci(2n+2)-n.

G.f.: (1-2x+2x^2)/((1-x)^2(1-3x+x^2)).

PROG

(PARI) Vec((1-2*x+2*x^2)/((1-x)^2*(1-3*x+x^2)) + O(x^40)) \\ Michel Marcus, Feb 14 2016

CROSSREFS

Sequence in context: A138237 A121286 A072863 * A291733 A118046 A057153

Adjacent sequences:  A054960 A054961 A054962 * A054964 A054965 A054966

KEYWORD

nonn

AUTHOR

Emeric Deutsch, Jun 16 2001

STATUS

approved

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Last modified January 17 16:33 EST 2018. Contains 297822 sequences.