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A055847
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A second order recursive sequence.
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1
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1, 6, 49, 392, 3136, 25088, 200704, 1605632, 12845056, 102760448, 822083584, 6576668672, 52613349376, 420906795008, 3367254360064, 26938034880512, 215504279044096, 1724034232352768, 13792273858822144, 110338190870577152
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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COMMENTS
| For n>=2, a(n) is equal to the number of functions f:{1,2,...,n}->{1,2,3,4,5,6,7,8} such that for fixed, different x_1, x_2 in {1,2,...,n} and fixed y_1, y_2 in {1,2,3,4,5,6,7,8} we have f(x_1)<>y_1 and f(x_2)<> y_2. - Milan R. Janjic (agnus(AT)blic.net), Apr 19 2007
a(n) is the number of generalized compositions of n when there are 7*i-1 different types of i, (i=1,2,...). [From Milan R. Janjic (agnus(AT)blic.net), Aug 26 2010]
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REFERENCES
| A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, pps. 194-196.
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LINKS
| Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets
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FORMULA
| a(n)=49*8^(n-2), a(0)=1, a(1)=6. a(n)=8a(n-1)+[(-1)^n]*C(2, 2-n); G.f.(x)=(1-x)^2/(1-8x).
a(n) = Sum_{k, 0<=k<=n} A201780(n,k)*6^k. - DELEHAM Philippe, Dec 05 2011
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CROSSREFS
| First differences of A055274. Cf. A001018.
Sequence in context: A097299 A104170 A098306 * A143165 A008786 A046195
Adjacent sequences: A055844 A055845 A055846 * A055848 A055849 A055850
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KEYWORD
| easy,nonn
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AUTHOR
| Barry E. Williams, Jun 03 2000
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EXTENSIONS
| More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jun 05 2000
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