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Search: id:A026549
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| A026549 |
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Ratios of successive terms are 2,3,2,3,2,3,2,3... |
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+0
3
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| 1, 2, 6, 12, 36, 72, 216, 432, 1296, 2592, 7776, 15552, 46656, 93312, 279936, 559872, 1679616, 3359232, 10077696, 20155392, 60466176, 120932352, 362797056, 725594112, 2176782336, 4353564672, 13060694016, 26121388032
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Appears to be the number of permutations p of {1,2,...,n} such that p(i)+p(i+1)>=n for every i=1,2,...,n-1 (if offset is 1). - Vladeta Jovovic (vladeta(AT)Eunet.yu), Dec 15 2003
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FORMULA
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Equals T(n, 0) + T(n, 1) + ... + T(n, 2n), T given by A026536.
G.f.: (1+2x)/(1-6x^2) - Paul Barry (pbarry(AT)wit.ie), Aug 25 2003
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CROSSREFS
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For n>0, a(n) = 2*A026532(n). Cf. A026551, A026567.
Sequence in context: A088808 A076278 A099576 this_sequence A120766 A121404 A074442
Adjacent sequences: A026546 A026547 A026548 this_sequence A026550 A026551 A026552
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KEYWORD
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nonn
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AUTHOR
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Clark Kimberling (ck6(AT)evansville.edu)
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EXTENSIONS
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New definition from Ralf Stephan, Dec 01, 2004
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