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Search: id:A081875
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| A081875 |
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Sum(d|n, phi(n/d) C(2*d,d) /2). |
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+0
1
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| 1, 4, 12, 40, 130, 480, 1722, 6480, 24336, 92520, 352726, 1352640, 5200312, 20060040, 77559060, 300546720, 1166803126, 4537592928, 17672631918, 68923357200, 269128940724, 1052049834616, 4116715363822, 16123803207552
(list; graph; listen)
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OFFSET
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1,2
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LINKS
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V. A. Liskovets, Enumerative formulae for unrooted planar maps: a pattern, Electron. J. Combin., 11:1 (2004), R88. v11i1r88.pdf
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MATHEMATICA
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Table[Fold[ #1+EulerPhi[n/#2]*Binomial[2#2, #2]/2&, 0, Divisors[n]], {n, 1, 32}]
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CROSSREFS
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Cf. A045630.
Sequence in context: A090576 A152174 A087206 this_sequence A102433 A100320 A064649
Adjacent sequences: A081872 A081873 A081874 this_sequence A081876 A081877 A081878
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KEYWORD
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easy,nonn
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AUTHOR
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Wouter Meeussen (wouter.meeussen(AT)pandora.be), Apr 12 2003
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