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A053157
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Number of 3-element intersecting families (with not necessary distinct sets) whose union is an n-element set.
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1
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1, 5, 32, 235, 1816, 14055, 107052, 800315, 5886416, 42739855, 307295572, 2193374595, 15571898616, 110121224855, 776543100092, 5464689616075, 38398915520416, 269529406433055, 1890416947176612, 13251578251332755
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OFFSET
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1,2
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REFERENCES
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V. Jovovic, G. Kilibarda, On the number of Boolean functions in the Post classes F^{mu}_8, Diskretnaya Matematika, 11 (1999), no. 4, 127-138 (translated in Discrete Mathematics and Applications, 9, (1999), no. 6).
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LINKS
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Table of n, a(n) for n=1..20.
Index to sequences with linear recurrences with constant coefficients, signature (22,-190,820,-1849,2038,-840).
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FORMULA
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a(n) = 1/3!*(7^n-3*5^n+3*4^n+2*3^n-3*2^n+2).
G.f.: -x*(280*x^5-475*x^4+339*x^3-112*x^2+17*x-1)/((x-1)*(2*x-1)*(3*x-1)*(4*x-1)*(5*x-1)*(7*x-1)). [Colin Barker, Jul 29 2012]
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CROSSREFS
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Cf. A051180.
Sequence in context: A065071 A153396 A146965 * A102231 A127089 A208046
Adjacent sequences: A053154 A053155 A053156 * A053158 A053159 A053160
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KEYWORD
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easy,nonn
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AUTHOR
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Vladeta Jovovic, Goran Kilibarda (vladeta(AT)eunet.rs), Feb 28 2000
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STATUS
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approved
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