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Search: id:A050488
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| 0, 1, 5, 15, 37, 83, 177, 367, 749, 1515, 3049, 6119, 12261, 24547, 49121, 98271, 196573, 393179, 786393, 1572823, 3145685, 6291411, 12582865, 25165775, 50331597, 100663243, 201326537, 402653127, 805306309, 1610612675, 3221225409
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OFFSET
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0,3
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COMMENT
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Number of words of length n+1 where first element is from {0,1,2}, other elements are from {0,1}, and sequence does not decrease (for n=2 there are 3*2^2 sequences, but 000,100,110,111,200,210,211 decrease, so a(2) = 12-7 = 5).
Number of subgroups of C_(2^n) X C_(2^n) (see A060724).
Starting with "1" = row sums of triangle A054582. - Gary W. Adamson (qntmpkt(AT)yahoo.com), Jun 23 2008
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FORMULA
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Row sums of A125165: (1, 5, 15, 37...). Binomial transform of [1, 4, 6, 6, 6...] = [1, 5, 15, 37,...]. 4-th diagonal from the right of A126777 = (1, 5, 15,...). - Gary W. Adamson (qntmpkt(AT)yahoo.com), Dec 23 2006
a(n) = 2*a(n-1) + (2n-1); e.g. a(4) = 37 = 2*15 + 7. - Gary W. Adamson (qntmpkt(AT)yahoo.com), Sep 30 2007
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CROSSREFS
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A050487(2^m-1).
Equals (1/2) A051667.
Cf. A126277, A125165.
Cf. A054852.
Sequence in context: A137609 A109818 A005491 this_sequence A014316 A075717 A062487
Adjacent sequences: A050485 A050486 A050487 this_sequence A050489 A050490 A050491
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KEYWORD
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nonn
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AUTHOR
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James A. Sellers (sellersj(AT)math.psu.edu), Dec 26, 1999.
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