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Search: id:A131708
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| 0, 1, 2, 3, 5, 10, 21, 43, 86, 171, 341, 682, 1365, 2731, 5462, 10923, 21845, 43690, 87381, 174763, 349526, 699051, 1398101, 2796202, 5592405, 11184811, 22369622, 44739243, 89478485, 178956970, 357913941, 715827883, 1431655766, 2863311531, 5726623061, 11453246122
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OFFSET
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0,3
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COMMENT
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Sequence is identical to its 3rd differences. a(n)=3a(n-1)-3a(n-2)+2a(n-2), n=3,4.. Also binomial transform of 0, 1, 0. Also A024495 = first differences. Recurrence: a(n+1)-2a(n)= 1, 0, -1, -1, 0, 1, 1 .
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FORMULA
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G.f.: x*(-1+x)/(2*x-1)/(x^2-x+1). - R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Nov 14 2007
Recurrences: a(n) = k*a(n - 1) + (6 - 3k)*a(n - 2) + (3k - 7)*a(n - 3) + (6 - 2k)*a(n - 4);k = 0: a(n) = 6a(n - 2) - 7a(n - 3) + 6a(n - 4), k = 1: a(n) = a(n - 1) + 3a(n - 2) - 4a(n - 3) + 4a(n - 4), k = 2: a(n) = 2a(n - 1) - a(n - 3) + 2a(n - 4), cf. A113405, A135350, k = 3: a(n) = 3a(n - 1) - 3a(n - 2) + 2a(n - 3), here and many other sequences, k = 4: a(n) = 4a(n - 1) - 6a(n - 2) + 5a(n - 3) - 2a(n - 4), k = 5: a(n) = 5a(n - 1) - 9a(n - 2) + 8a(n - 3) - 4a(n - 4). For k sum of cofficients = 5 - k. Of the family k=3 gives the best recurrence.
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CROSSREFS
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Sequence in context: A014626 A132418 A024494 this_sequence A002991 A022861 A001646
Adjacent sequences: A131705 A131706 A131707 this_sequence A131709 A131710 A131711
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KEYWORD
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nonn
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AUTHOR
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Paul Curtz (bpcrtz(AT)free.fr), Sep 14 2007, Mar 01 2008
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