

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
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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^2x^3+x^4) / ( (1+x)^2*(x1)^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



