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 A056002 a(n) = (10^2)*11^(n-2); a(0)=1, a(1)=9. 2
 1, 9, 100, 1100, 12100, 133100, 1464100, 16105100, 177156100, 1948717100, 21435888100, 235794769100, 2593742460100, 28531167061100, 313842837672100, 3452271214393100, 37974983358324100, 417724816941565100 (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}->{1,2,3,4,5,6,7,8,9,10,11} such that for fixed, different x_1, x_2 in {1,2,...,n} and fixed y_1, y_2 in {1,2,3,4,5,6,7,8,9,10,11} 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 10*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)=11a(n-1)+[(-1)^n]*C(2, 2-n). G.f.(x)=(1-x)^2/(1-11x). a(n) = Sum_{k, 0<=k<=n} A201780(n,k)*9^k. - Philippe Deléham, Dec 05 2011 MATHEMATICA Join[{1, 9}, 100*11^Range[0, 20]] (* or *) Join[{1, 9}, NestList[11#&, 100, 20]] (* Harvey P. Dale, May 24 2012 *) CROSSREFS Cf. A001020. Sequence in context: A266098 A065736 A092936 * A060150 A202833 A287039 Adjacent sequences:  A055999 A056000 A056001 * A056003 A056004 A056005 KEYWORD easy,nonn AUTHOR Barry E. Williams, Jun 18 2000 EXTENSIONS More terms from James A. Sellers, Jul 04 2000 STATUS approved

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Last modified May 14 18:51 EDT 2021. Contains 343900 sequences. (Running on oeis4.)