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A070252
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Number of n-digit palindromes.
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7
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10, 9, 90, 90, 900, 900, 9000, 9000, 90000, 90000, 900000, 900000, 9000000, 9000000, 90000000, 90000000, 900000000, 900000000, 9000000000, 9000000000, 90000000000, 90000000000, 900000000000, 900000000000, 9000000000000
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OFFSET
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1,1
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LINKS
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Table of n, a(n) for n=1..25.
Index entries for linear recurrences with constant coefficients, signature (0,10).
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FORMULA
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From Colin Barker, Aug 19 2013: (Start)
a(n) = 10*a(n-2) for n>3.
G.f.: x*(10*x^2-9*x-10) / (10*x^2-1). (End)
E.g.f.: x + 9*(cosh(sqrt(10)*x) - 1 + sqrt(10)*sinh(sqrt(10)*x))/10. - Stefano Spezia, Jun 11 2022
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MATHEMATICA
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LinearRecurrence[{0, 10}, {10, 9, 90}, 25] (* Stefano Spezia, Jun 11 2022 *)
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CROSSREFS
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A variant of A050683, which is the principal entry for this sequence. Cf. A016115.
Partial sums give A070199.
Sequence in context: A241285 A052196 A243035 * A038311 A244960 A282560
Adjacent sequences: A070249 A070250 A070251 * A070253 A070254 A070255
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KEYWORD
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base,nonn,easy
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AUTHOR
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Amarnath Murthy, May 06 2002
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STATUS
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approved
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