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%I #13 Apr 27 2020 14:01:58
%S 0,1,2,3,4,10,12,21,32,53,128,213,512,853,2048,3413,8192,13653,32768,
%T 54613,131072,218453,524288,873813,2097152,3495253,8388608,13981013,
%U 33554432,55924053,134217728,223696213,536870912,894784853,2147483648
%N a(n+1) = smallest number not containing any digits of a(n), working in base 4.
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (0,5,0,-4).
%F For n>9, a(n)=4*a(n-2) + (a(n-2) mod 4).
%F a(n) = 5*a(n-2)-4*a(n-4) for n>5; g.f.: x*(32*x^10+16*x^9-12*x^8-12*x^7-17*x^6-x^4-6*x^3-2*x^2+2*x+1) / ((x-1)*(x+1)*(2*x-1)*(2*x+1)). - _Colin Barker_, Sep 13 2014
%e Written in base 4 the sequence appears as 0, 1, 2, 3, 10, 22, 30, 111, 200, 311, 2000, 3111, 20000, 31111, 200000, 311111, 2000000, 3111111, etc. So a(9)=311 base 4 =53 base 10.
%t LinearRecurrence[{0,5,0,-4},{0,1,2,3,4,10,12,21,32,53,128,213},40] (* _Harvey P. Dale_, Apr 27 2020 *)
%Y Cf. A030283, A030439.
%K base,easy,nonn
%O 0,3
%A _Henry Bottomley_, Dec 28 2000
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