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 A055995 a(n) = 64*9^(n-2), a(0)=1, a(1)=7. 2
 1, 7, 64, 576, 5184, 46656, 419904, 3779136, 34012224, 306110016, 2754990144, 24794911296, 223154201664, 2008387814976, 18075490334784, 162679413013056, 1464114717117504, 13177032454057536, 118593292086517824 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS For n>=2, a(n) is equal to the number of functions f:{1,2,...,n}->{1,2,3,4,5,6,7,8,9} such that for fixed, different x_1, x_2 in {1,2,...,n} and fixed y_1, y_2 in {1,2,3,4,5,6,7,8,9} we have f(x_1)<>y_1 and f(x_2)<> y_2. - Milan Janjic, Apr 19 2007 a(n) is the number of generalized compositions of n when there are 8*i-1 different types of i, (i=1,2,...). - Milan Janjic, Aug 26 2010 REFERENCES A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, pp. 194-196. LINKS Milan Janjic, Enumerative Formulas for Some Functions on Finite Sets FORMULA a(n) = 9a(n-1) + ((-1)^n)*C(2, 2-n). G.f.: (1-x)^2/(1-9x). a(n) = Sum_{k, 0<=k<=n} A201780(n,k)*7^k. - Philippe Deléham, Dec 05 2011 CROSSREFS Second differences of 9^n (A001019). Cf. A055275. Sequence in context: A333991 A159617 A098307 * A301424 A288690 A213515 Adjacent sequences:  A055992 A055993 A055994 * A055996 A055997 A055998 KEYWORD easy,nonn AUTHOR Barry E. Williams, Jun 04 2000 STATUS approved

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Last modified December 3 21:17 EST 2021. Contains 349468 sequences. (Running on oeis4.)