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A062553
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Number of Abelian subgroups of the dihedral group with 2n elements.
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1
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2, 5, 5, 9, 7, 13, 9, 16, 12, 19, 13, 24, 15, 25, 19, 29, 19, 33, 21, 36, 25, 37, 25, 44, 28, 43, 31, 48, 31, 53, 33, 54, 37, 55, 39, 63, 39, 61, 43, 68, 43, 71, 45, 72, 51, 73, 49, 82, 52, 81, 55, 84, 55, 89, 59, 92, 61, 91, 61, 102, 63, 97, 69, 103, 69, 107, 69, 108, 73
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OFFSET
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1,1
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COMMENTS
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The rank of the fundamental group with genus one of the D_2n; cobordism category in dimension 1+1, with D_2n the dihedral group of order 2n. - _C. Segovia_, Dec 05 2012
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LINKS
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FORMULA
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a(n) = n + tau(n) if n is odd, (3/2)*n + tau(n) if n is even, where tau(n) = the number of divisors of n (A000005).
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MATHEMATICA
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a[n_] := If[OddQ[n], n, 3n/2] + DivisorSigma[0, n];
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CROSSREFS
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KEYWORD
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nonn
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AUTHOR
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Ahmed Fares (ahmedfares(AT)my-deja.com), Jul 02 2001
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EXTENSIONS
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STATUS
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approved
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