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A126639 a(n) is the number of integers k less than 10^n such that the decimal representation of k lacks the digit 1,2,3, at least one of digits 4,5,6 and at least one of digits 7,8,9.

%I A126639 #12 Aug 12 2015 16:16:13
%S A126639 7,49,331,2137,13147,77449,440251,2432857,13151707,69895849,366600571,
%T A126639 1903222777,9802234267,50171448649,255545887291,1296626911897,
%U A126639 6559153748827,33101134543849,166731005404411,838567970940217,4212526479343387,21141483461069449
%N A126639 a(n) is the number of integers k less than 10^n such that the decimal representation of k lacks the digit 1,2,3, at least one of digits 4,5,6 and at least one of digits 7,8,9.
%H A126639 Colin Barker, <a href="/A126639/b126639.txt">Table of n, a(n) for n = 1..1000</a>
%H A126639 Milan Janjic, <a href="http://www.pmfbl.org/janjic/">Enumerative Formulas for Some Functions on Finite Sets</a>
%H A126639 <a href="/index/Rec#order_05">Index entries for linear recurrences with constant coefficients</a>, signature (15,-85,225,-274,120).
%F A126639 a(n) = 9*5^n-18*4^n+15*3^n-6*2^n+1.
%F A126639 G.f.: -x*(120*x^4-238*x^3+191*x^2-56*x+7) / ((x-1)*(2*x-1)*(3*x-1)*(4*x-1)*(5*x-1)). - _Colin Barker_, Feb 22 2015
%p A126639 f:=n->9*5^n-18*4^n+15*3^n-6*2^n+1;
%t A126639 LinearRecurrence[{15,-85,225,-274,120},{7,49,331,2137,13147},30] (* _Harvey P. Dale_, Aug 12 2015 *)
%o A126639 (PARI) Vec(-x*(120*x^4-238*x^3+191*x^2-56*x+7) / ((x-1)*(2*x-1)*(3*x-1)*(4*x-1)*(5*x-1)) + O(x^100)) \\ _Colin Barker_, Feb 22 2015
%Y A126639 Cf. A125630, A125948, A125947, A125946, A125945, A125940, A125909, A125908, A125880, A125897, A125904, A125858.
%K A126639 nonn,base,easy
%O A126639 1,1
%A A126639 Aleksandar M. Janjic and _Milan Janjic_, Feb 08 2007