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A095153
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Number of 4-block covers of a labeled n-set.
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1
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35, 1225, 24990, 426650, 6779185, 104394675, 1585021340, 23909487700, 359582866335, 5400330984125, 81051093085690, 1216089331752750, 18243600636165485, 273669834496409575, 4105158293128058040, 61578149829707541800, 923677675484159636635
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OFFSET
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3,1
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LINKS
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FORMULA
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a(n) = (1/4!)*(-50+35*3^n-10*7^n+15^n).
G.f.: 35*x^3*(9*x+1) / ((x-1)*(3*x-1)*(7*x-1)*(15*x-1)). - Colin Barker, Jul 13 2013
a(n) = Sum_{i=0..n} (-1)^i * C(n,i) * C(2^(n-i)-1,4). - Geoffrey Critzer, Aug 24 2014
a(n) = 26*a(n-1)-196*a(n-2)+486*a(n-3)-315*a(n-4). - Wesley Ivan Hurt, Aug 26 2014
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MAPLE
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MATHEMATICA
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nn = 19; Table[Sum[(-1)^i Binomial[n, i] Binomial[2^(n - i) - 1, 4], {i, 0, n}], {n, 3, nn}] (* Geoffrey Critzer, Aug 24 2014 *)
Table[(-50 + 35*3^n - 10*7^n + 15^n)/24, {n, 3, 20}] (* Wesley Ivan Hurt, Aug 26 2014 *)
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PROG
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(Magma) [(-50 + 35*3^n - 10*7^n + 15^n)/24 : n in [3..20]]; // Wesley Ivan Hurt, Aug 26 2014
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CROSSREFS
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KEYWORD
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easy,nonn
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AUTHOR
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EXTENSIONS
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STATUS
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approved
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