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 A135342 Number of distinct means of subsets of {1,...,n}. 0
 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; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA 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 EXAMPLE 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} MATHEMATICA a[n_] := Sum[EulerPhi[k] (n - k), {k, 1, n - 1}] + Min[n, 2] CROSSREFS Second differences are A000010. Sequence in context: A003593 A120027 A018586 * A029877 A207641 A147425 Adjacent sequences:  A135339 A135340 A135341 * A135343 A135344 A135345 KEYWORD easy,nonn AUTHOR Jacob A. Siehler, Feb 16 2008 STATUS approved

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