A056002 a(n) = (10^2)*11^(n-2); a(0)=1, a(1)=9.

1, 9, 100, 1100, 12100, 133100, 1464100, 16105100, 177156100, 1948717100, 21435888100, 235794769100, 2593742460100, 28531167061100, 313842837672100, 3452271214393100, 37974983358324100, 417724816941565100

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

Table of n, a(n) for n=0..17.

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 A356131

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