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A007238
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Length of longest chain of subgroups in S_n.
(Formerly M0945)
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3
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0, 1, 2, 4, 5, 6, 7, 10, 11, 12, 13, 15, 16, 17, 18, 22, 23, 24, 25, 27, 28, 29, 30, 33, 34, 35, 36, 38, 39, 40, 41, 46, 47, 48, 49, 51, 52, 53, 54, 57, 58, 59, 60, 62, 63, 64, 65, 69, 70, 71, 72, 74, 75, 76, 77, 80, 81, 82, 83, 85, 86, 87, 88, 94, 95, 96, 97, 99, 100, 101
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OFFSET
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1,3
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COMMENTS
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Starting at a(2), this is column 2 of Table 1 of the Donald M. Davis paper, p.32. - Jonathan Vos Post, Jul 17 2008
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REFERENCES
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N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
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LINKS
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P. J. Cameron, M. Gadouleau, J. D. Mitchell, Y. Peresse, Chains of subsemigroups, arXiv preprint arXiv:1501.06394 [math.GR], 2015.
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FORMULA
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a(n) = ceiling(3n/2) - b(n) - 1, where b(n) = # 1's in binary expansion of n (A000120).
G.f.: 1/(1-x) * (-1/(1-x^2) + Sum(k>=0, x^2^k/(1-x^2^k))). - Ralf Stephan, Apr 13 2002
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MAPLE
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convert(n, base, 2) ;
add(i, i=%) ;
end proc:
end proc:
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MATHEMATICA
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a[n_] := Ceiling[ 3n/2 ] - Count[ IntegerDigits[n, 2], 1] - 1; Table[ a[n], {n, 1, 70}] (* Jean-François Alcover, Jan 19 2012, after formula *)
Table[Ceiling[(3n)/2]-DigitCount[n, 2, 1]-1, {n, 70}] (* Harvey P. Dale, Nov 20 2021 *)
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PROG
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(PARI) vector(70, n, ceil(3*n/2) - hammingweight(n) - 1) \\ Joerg Arndt, May 16 2016
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CROSSREFS
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KEYWORD
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nonn,nice
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AUTHOR
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STATUS
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approved
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