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A126645 a(n) is the number of integers k less than 10^n such that the decimal representation of k lacks the digits 1,2,3,4 and 5, at least one of digits 6,7 and at least one of digits 8,9.

%I A126645 #15 Jun 13 2015 00:52:18
%S A126645 5,21,77,261,845,2661,8237,25221,76685,232101,700397,2109381,6344525,
%T A126645 19066341,57264557,171924741,516036365,1548633381,4646948717,
%U A126645 13942943301,41833024205,125507461221,376539160877,1129651037061,3389020220045,10167194877861
%N A126645 a(n) is the number of integers k less than 10^n such that the decimal representation of k lacks the digits 1,2,3,4 and 5, at least one of digits 6,7 and at least one of digits 8,9.
%H A126645 Colin Barker, <a href="/A126645/b126645.txt">Table of n, a(n) for n = 1..1000</a>
%H A126645 Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas for Some Functions on Finite Sets</a>
%H A126645 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (6,-11,6).
%F A126645 a(n) = 4*3^n-4*2^n+1.
%F A126645 a(n) = 6*a(n-1)-11*a(n-2)+6*a(n-3). - _Colin Barker_, Feb 22 2015
%F A126645 G.f.: -x*(6*x^2-9*x+5) / ((x-1)*(2*x-1)*(3*x-1)). - _Colin Barker_, Feb 22 2015
%p A126645 f:=n->4*3^n-4*2^n+1;
%o A126645 (PARI) Vec(-x*(6*x^2-9*x+5)/((x-1)*(2*x-1)*(3*x-1)) + O(x^100)) \\ _Colin Barker_, Feb 22 2015
%Y A126645 Cf. A125630, A125948, A125947, A125946, A125945, A125940, A125909, A125908, A125880, A125897, A125904, A125858.
%K A126645 nonn,base,easy
%O A126645 1,1
%A A126645 Aleksandar M. Janjic and _Milan Janjic_, Feb 08 2007