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A055796
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T(2n+3,n), array T as in A055794.
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6
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1, 5, 16, 42, 98, 210, 420, 792, 1419, 2431, 4004, 6370, 9828, 14756, 21624, 31008, 43605, 60249, 81928, 109802, 145222, 189750, 245180, 313560, 397215, 498771, 621180, 767746, 942152, 1148488, 1391280, 1675520, 2006697, 2390829, 2834496, 3344874, 3929770
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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>=6, a(n-6) is the number of 6-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) = (n+1)(n+2)(n+3)(n+4)(n^2-n+30)/720.
a(n-4) = binomial(n,6) + binomial(n,4) for n>3. - Zerinvary Lajos, Jul 24 2006
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MAPLE
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seq(binomial(n+4, 6)+binomial(n+4, 4), n=0..33) # Zerinvary Lajos, Jul 24 2006
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MATHEMATICA
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LinearRecurrence[{7, -21, 35, -35, 21, -7, 1}, {1, 5, 16, 42, 98, 210, 420}, 50] (* Vincenzo Librandi, Apr 30 2012 *)
Table[(n+1)(n+2)(n+3)(n+4)(n^2-n+30)/720, {n, 0, 50}] (* Harvey P. Dale, Feb 12 2013 *)
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PROG
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(Magma) [(n+1)*(n+2)*(n+3)*(n+4)*(n^2-n+30)/720: n in [0..40]]; // Vincenzo Librandi, Apr 30 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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EXTENSIONS
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STATUS
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approved
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