%I A055270
%S A055270 1,5,36,252,1764,12348,86436,605052,4235364,29647548,207532836,
%T A055270 1452729852,10169108964,71183762748,498286339236,3488004374652,
%U A055270 24416030622564,170912214357948,1196385500505636,8374698503539452
%N A055270 a(n)=7a(n-1)+(-1^n)*binomial(2,2-n); a(-1)=0.
%C A055270 For n>=2, a(n) is equal to the number of functions f:{1,2,...,n}->{1,
               2,3,4,5,6,7} 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} we have f(x_1)<>y_1 and 
               f(x_2)<> y_2. - Milan R. Janjic (agnus(AT)blic.net), Apr 19 2007
%D A055270 A. H. Beiler, Recreations in the Theory of Numbers, Dover, N.Y., 1964, 
               pps. 122-125, 194-196.
%H A055270 Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas 
               for Some Functions on Finite Sets</a>
%F A055270 a(n)=(6^2)*(7^(n-2)), n >= 2; a(0)=1, a(1)=5. G.f.(x)=(1-x)^2/(1-7x).
%Y A055270 Cf. A052268 and A011557. Second differences of A000420.
%Y A055270 Sequence in context: A015547 A067376 A098305 this_sequence A164110 A052203 
               A027331
%Y A055270 Adjacent sequences: A055267 A055268 A055269 this_sequence A055271 A055272 
               A055273
%K A055270 easy,nonn
%O A055270 0,2
%A A055270 Barry E. Williams, May 10 2000
%E A055270 More terms from James A. Sellers (sellersj(AT)math.psu.edu), May 22 2000