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A031940 Length of longest legal domino snake using full set of dominoes up to [n:n]. 2
1, 3, 6, 9, 15, 19, 28, 33, 45, 51, 66, 73, 91, 99, 120, 129, 153, 163, 190, 201, 231, 243, 276, 289, 325, 339, 378, 393, 435, 451, 496, 513, 561, 579, 630, 649, 703, 723, 780, 801 (list; graph; refs; listen; history; text; internal format)
OFFSET

1,2

COMMENTS

a(n) = A204556(n+1) / (n+1). [Reinhard Zumkeller, Jan 18 2012]

LINKS

Table of n, a(n) for n=1..40.

Index entries for sequences related to dominoes

Index entries for linear recurrences with constant coefficients, signature (1,2,-2,-1,1).

FORMULA

C(n, 2)+n if n odd, C(n, 2)+n/2+1 if n even. - T. D. Noe, Nov 09 2006

G.f. -x*(1+2*x+x^2-x^3+x^4) / ( (1+x)^2*(x-1)^3 ). - R. J. Mathar, Aug 13 2012

EXAMPLE

E.g. for n=4 [ 1:1 ][ 1:2 ][ 2:2 ][ 2:3 ][ 3:3 ][ 3:1 ][ 1:4 ][ 4:4 ][ 4:2 ].

CROSSREFS

Cf. A031878.

Sequence in context: A133205 A049991 A143981 * A007187 A082004 A112773

Adjacent sequences:  A031937 A031938 A031939 * A031941 A031942 A031943

KEYWORD

nonn

AUTHOR

Colin Mallows

EXTENSIONS

Corrected by T. D. Noe, Nov 09 2006

STATUS

approved

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Last modified August 28 10:44 EDT 2015. Contains 261120 sequences.