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A247415
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Number of friezes of type D_n.
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1
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1, 4, 14, 51, 187, 695, 2606, 9842, 37386, 142693, 546790, 2102312, 8106308, 31335060, 121390028, 471159761, 1831860961, 7133082300, 27813493104, 108585087657, 424396534100, 1660418620528, 6502345229958, 25485677806201, 99969379431223, 392424954930562, 1541494622610616, 6059022365002926, 23829761312067896
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OFFSET
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1,2
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LINKS
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FORMULA
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a(n) = sum_{m=1..n} A000005(m)*binomial(2n-m-1,n-m).
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MAPLE
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a:= n -> add(numtheory:-tau(m)*binomial(2*n-m-1, n-m), m=1..n):
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MATHEMATICA
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a[n_] := Sum[DivisorSigma[0, m] Binomial[2n-m-1, n m], {m, 1, n}]
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PROG
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(PARI) a(n) = sum(m=1, n, numdiv(m)*binomial(2*n-m-1, n-m) ); \\ Joerg Arndt, Sep 16 2014
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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STATUS
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approved
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