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A190331
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a(n) = 8*a(n-1) + 2*a(n-2), with a(0)=0, a(1)=1.
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2
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0, 1, 8, 66, 544, 4484, 36960, 304648, 2511104, 20698128, 170607232, 1406254112, 11591247360, 95542487104, 787522391552, 6491264106624, 53505157636096, 441023789302016, 3635200629688320, 29963652616110592, 246979622188261376, 2035764282738312192
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OFFSET
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0,3
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COMMENTS
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For n>0, a(n) equals the number of words of length n-1 over {0,1,...,9} in which 0 and 1 avoid runs of odd lengths. - Milan Janjic, Jan 08 2017
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LINKS
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FORMULA
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MATHEMATICA
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LinearRecurrence[{8, 2}, {0, 1}, 50]
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PROG
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(PARI) x='x+O('x^30); concat([0], Vec(x/(1-8*x-2*x^2))) \\ G. C. Greubel, Jan 24 2018
(Magma) I:=[0, 1]; [n le 2 select I[n] else 8*Self(n-1) + 2*Self(n-2): n in [1..30]]; // G. C. Greubel, Jan 24 2018
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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