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A117857
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Number of palindromes of length n (in base 5).
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1
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4, 4, 20, 20, 100, 100, 500, 500, 2500, 2500, 12500, 12500, 62500, 62500, 312500, 312500, 1562500, 1562500, 7812500, 7812500, 39062500, 39062500, 195312500, 195312500, 976562500, 976562500, 4882812500, 4882812500, 24414062500, 24414062500, 122070312500
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OFFSET
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1,1
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LINKS
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FORMULA
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a(n) = 4*5^floor((n-1)/2).
a(n) = 5*a(n-2). G.f.: -4*x*(x+1)/(5*x^2-1). [Colin Barker, Feb 15 2013]
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MAPLE
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MATHEMATICA
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LinearRecurrence[{0, 5}, {4, 4}, 40] (* or *) With[{c=NestList[ 5#&, 4, 20]}, Riffle[ c, c]] (* Harvey P. Dale, Apr 18 2019 *)
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CROSSREFS
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KEYWORD
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nonn,base,easy
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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