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%I #9 Mar 03 2024 14:38:57
%S 1,4,7,19,49,79,199,499,799,1999,4999,7999,19999,49999,79999,199999,
%T 499999,799999,1999999,4999999,7999999,19999999,49999999,79999999,
%U 199999999,499999999,799999999,1999999999,4999999999,7999999999
%N Smallest number whose sum of digits is 3n+1.
%H <a href="/index/Rec#order_04">Index entries for linear recurrences with constant coefficients</a>, signature (1, 0, 10, -10).
%F a(n) = a(n-1) + 10*a(n-3) - 10*a(n-4). - _Chai Wah Wu_, May 25 2016
%F G.f.: (1 + 3*x + 3*x^2 + 2*x^3)/(1 - x - 10*x^3 + 10*x^4). - _Michael De Vlieger_, May 25 2016
%t LinearRecurrence[{1, 0, 10, -10}, {1, 4, 7, 19}, 31] (* or *)
%t CoefficientList[Series[(1 + 3 x + 3 x^2 + 2 x^3)/(1 - x - 10 x^3 + 10 x^4), {x, 0, 30}], x] (* _Michael De Vlieger_, May 25 2016 *)
%K nonn,base
%O 0,2
%A _Paul Curtz_, Oct 16 2007
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