This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A056002 #18 Jul 02 2025 16:02:00
%S A056002 1,9,100,1100,12100,133100,1464100,16105100,177156100,1948717100,
%T A056002 21435888100,235794769100,2593742460100,28531167061100,
%U A056002 313842837672100,3452271214393100,37974983358324100,417724816941565100
%N A056002 a(n) = (10^2)*11^(n-2); a(0)=1, a(1)=9.
%C A056002 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
%C A056002 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
%D A056002 A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, pp. 194-196.
%H A056002 Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas for Some Functions on Finite Sets</a>
%F A056002 a(n)=11a(n-1)+[(-1)^n]*C(2, 2-n). G.f.(x)=(1-x)^2/(1-11x).
%F A056002 a(n) = Sum_{k, 0<=k<=n} A201780(n,k)*9^k. - _Philippe Deléham_, Dec 05 2011
%t A056002 Join[{1,9},100*11^Range[0,20]] (* or *) Join[{1,9},NestList[11#&,100,20]] (* _Harvey P. Dale_, May 24 2012 *)
%Y A056002 Cf. A001020.
%K A056002 easy,nonn
%O A056002 0,2
%A A056002 _Barry E. Williams_, Jun 18 2000
%E A056002 More terms from _James Sellers_, Jul 04 2000