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Search: id:A138977
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| A138977 |
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Number of 2 X n matrices containing a 1 in the top left entry, all entries are integer values and adjacent entries differ by at most 1. |
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3
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| 3, 19, 121, 771, 4913, 31307, 199497, 1271251, 8100769, 51620379, 328939577, 2096095523, 13356910353, 85113990379, 542370291241, 3456136077171, 22023471375233, 140339755317947, 894284401724697, 5698631790801091, 36313284928708849, 231398467337757579
(list; graph; listen)
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OFFSET
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1,1
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COMMENT
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Horizontally or vertically adjacent entries can differ by at most 1. Diagonally adjacent entries thus differ by at most 2.
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FORMULA
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a(n)=b(n)+c(n), where b(1)=2, c(1)=1, b(n+1)=4*b(n)+4*c(n), c(n+1)=2*b(n)+3*c(n).
G.f.: (3-2*x)/(1-7*x+4*x^2). - N. J. A. Sloane (njas(AT)research.att.com), Apr 06 2008
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EXAMPLE
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a(1) = 3:
|1|1|1|
|0|1|2|
a(2) = 19:
|10|11|12| |10|11|12| |10|11|12|
|0*|0*|01| |1*|1*|1*| |21|2*|2*|
(3) (2)(1) (2) (3)(2) (1) (2)(3), total 19
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CROSSREFS
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Cf. A138978, A138979.
Sequence in context: A139176 A126809 A020073 this_sequence A163605 A074572 A157455
Adjacent sequences: A138974 A138975 A138976 this_sequence A138978 A138979 A138980
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KEYWORD
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nonn,easy
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AUTHOR
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Wayne VanWeerthuizen (sequences(AT)waynemv.net), Apr 05 2008
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