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Search: id:A056182
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| 0, 2, 10, 38, 130, 422, 1330, 4118, 12610, 38342, 116050, 350198, 1054690, 3172262, 9533170, 28632278, 85962370, 258018182, 774316690, 2323474358, 6971471650, 20916512102, 62753730610, 188269580438, 564825518530
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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Let V be a binary relation on the power set P(A) of a set A having n = |A| elements such that for every element x, y of P(A), xVy if x is a proper subset of y or y is a proper subset of x. Then a(n) = |V|. - Ross La Haye (rlahaye(AT)new.rr.com), Dec 22 2006
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FORMULA
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2 * (3^n - 2^n).
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MATHEMATICA
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Table[ -((-1 + k)^(1-k+n)*(-1+k)!)+k^(-k+n)*k! /. k -> 3, {n, 3, 36} ]
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CROSSREFS
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3rd column of A056151.
A002783(n) - 1.
Adjacent sequences: A056179 A056180 A056181 this_sequence A056183 A056184 A056185
Sequence in context: A048499 A119358 A110148 this_sequence A081956 A120278 A143960
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KEYWORD
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nonn,easy
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AUTHOR
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njas, Aug 05 2000
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EXTENSIONS
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More terms from Wouter Meeussen (wouter.meeussen(AT)pandora.be), Aug 05 2000
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