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Search: id:A135342
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| A135342 |
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Number of distinct means of subsets of {1,...,n}. |
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+0
1
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| 1, 3, 5, 9, 15, 25, 37, 55, 77, 105, 137, 179, 225, 283, 347, 419, 499, 595, 697, 817, 945, 1085, 1235, 1407, 1587, 1787, 1999, 2229, 2471, 2741, 3019, 3327, 3651, 3995, 4355, 4739, 5135, 5567, 6017, 6491, 6981, 7511, 8053, 8637, 9241, 9869, 10519, 11215
(list; graph; listen)
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OFFSET
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1,2
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FORMULA
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a(n) = sum_{k=1}^{n-1} [(n-k) * phi(k)] + min(n,2); a(1)=1; a(2)=3; a(3)=5; a(n) = 2a(n-1)-a(n-2)+phi(n-1), n>3
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EXAMPLE
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a(4)=9: the possible means for a set drawn from {1,2,3,4} are {1,3/2,2,7/3,5/2,8/3,3,7/2,4}
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MATHEMATICA
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a[n_] := Sum[EulerPhi[k] (n - k), {k, 1, n - 1}] + Min[n, 2]
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CROSSREFS
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Second differences are A000010.
Sequence in context: A003593 A120027 A018586 this_sequence A029877 A128587 A080430
Adjacent sequences: A135339 A135340 A135341 this_sequence A135343 A135344 A135345
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KEYWORD
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easy,nonn
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AUTHOR
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Jacob A. Siehler (siehlerj(AT)wlu.edu), Feb 16 2008
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