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A257286
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a(n) = 5*6^n - 4*5^n.
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7
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1, 10, 80, 580, 3980, 26380, 170780, 1087180, 6835580, 42575980, 263268380, 1618672780, 9907349180, 60420657580, 367406757980, 2228854610380, 13495197974780, 81581539411180, 492540994279580, 2970504754739980, 17899322473752380
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OFFSET
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0,2
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COMMENTS
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First differences of 6^n - 5^n = A005062.
a(n-1) is the number of numbers with n digits having the largest digit equal to 5. Or, equivalently, number of n-letter words over a 6-letter alphabet {a,b,c,d,e,f}, which must not start with the first letter of the alphabet, and in which the last letter of the alphabet must appear.
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LINKS
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FORMULA
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a(n) = 11 a(n-1) - 30 a(n-2).
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MATHEMATICA
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PROG
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(PARI) a(n)=5*6^n-4*5^n
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CROSSREFS
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Coincides with A125373 only for the first terms.
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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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