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A055798
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T(2n+5,n), array T as in A055794.
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3
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1, 7, 29, 93, 255, 627, 1419, 3003, 6006, 11440, 20878, 36686, 62322, 102714, 164730, 257754, 394383, 591261, 870067, 1258675, 1792505, 2516085, 3484845, 4767165, 6446700, 8625006, 11424492, 14991724, 19501108, 25158980, 32208132, 40932804, 51664173
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OFFSET
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0,2
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COMMENTS
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If Y is a 2-subset of an n-set X then, for n>=8, a(n-8) is the number of 8-subsets of X which do not have exactly one element in common with Y. - Milan Janjic, Dec 28 2007
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LINKS
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FORMULA
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a(n-8) = binomial(n,8)-2*binomial(n-2,7), n=8,9,10,.... - Milan Janjic, Dec 28 2007
a(n) = 9*a(n-1) - 36*a(n-2) + 84*a(n-3) - 126*a(n-4) + 126*a(n-5) - 84*a(n-6) + 36*a(n-7) - 9*a(n-8) + a(n-9). - Vincenzo Librandi, May 01 2012
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MATHEMATICA
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LinearRecurrence[{9, -36, 84, -126, 126, -84, 36, -9, 1}, {1, 7, 29, 93, 255, 627, 1419, 3003, 6006}, 50] (* Vincenzo Librandi, May 01 2012 *)
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PROG
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(Magma) [Binomial(n, 8)-2*Binomial(n-2, 7): n in [8..40]]; // Vincenzo Librandi, May 01 2012
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CROSSREFS
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KEYWORD
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nonn,easy
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AUTHOR
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STATUS
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approved
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