Search: id:A055996
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%I A055996
%S A055996 1,8,81,810,8100,81000,810000,8100000,81000000,810000000,8100000000,
%T A055996 81000000000,810000000000,8100000000000,81000000000000,810000000000000,
%U A055996 8100000000000000,81000000000000000,810000000000000000
%N A055996 a(n)=81*10^(n-2), a(0)=1, a(1)=8.
%C A055996 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 R. Janjic (agnus(AT)blic.net), Apr 
               19 2007
%D A055996 A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, 
               pps. 194-196.
%H A055996 Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas 
               for Some Functions on Finite Sets</a>
%F A055996 a(n)=10a(n-1)+[(-1)^n]*C(2, 2-n). G.f.(x)=(1-x)^2/(1-10x).
%Y A055996 Second differences of 10^n (A011557). Cf. A052268.
%Y A055996 Sequence in context: A027768 A007792 A098308 this_sequence A068617 A007778 
               A065440
%Y A055996 Adjacent sequences: A055993 A055994 A055995 this_sequence A055997 A055998 
               A055999
%K A055996 easy,nonn
%O A055996 0,2
%A A055996 Barry E. Williams, Jun 04 2000
%E A055996 More terms from James A. Sellers (sellersj(AT)math.psu.edu), Jun 08 2000

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