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%I #20 Nov 20 2015 15:30:13
%S 1,8,81,810,8100,81000,810000,8100000,81000000,810000000,8100000000,
%T 81000000000,810000000000,8100000000000,81000000000000,
%U 810000000000000,8100000000000000,81000000000000000,810000000000000000
%N a(n) = 81*10^(n-2), a(0)=1, a(1)=8.
%C 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} 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} we have f(x_1)<>y_1 and f(x_2)<> y_2. - _Milan Janjic_, Apr 19 2007
%C a(n) is the number of generalized compositions of n when there are 9*i-1 different types of i, (i=1,2,...). - _Milan Janjic_, Aug 26 2010
%D A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, pp. 194-196.
%H Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas for Some Functions on Finite Sets</a>
%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (10)
%F a(n)=10a(n-1)+[(-1)^n]*C(2, 2-n). G.f.(x)=(1-x)^2/(1-10x).
%F a(n) = Sum_{k, 0<=k<=n} A201780(n,k)*8^k. - _Philippe Deléham_, Dec 05 2011
%t Join[{1,8},NestList[10#&,81,20]] (* _Harvey P. Dale_, Nov 20 2015 *)
%Y Second differences of 10^n (A011557). Cf. A052268.
%K easy,nonn
%O 0,2
%A _Barry E. Williams_, Jun 04 2000
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