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A086940 a(n) = k where R(k+4) = 2.

%I A086940 #20 May 01 2025 08:32:20
%S A086940 16,196,1996,19996,199996,1999996,19999996,199999996,1999999996,
%T A086940 19999999996,199999999996,1999999999996,19999999999996,
%U A086940 199999999999996,1999999999999996,19999999999999996,199999999999999996,1999999999999999996,19999999999999999996
%N A086940 a(n) = k where R(k+4) = 2.
%H A086940 Vincenzo Librandi, <a href="/A086940/b086940.txt">Table of n, a(n) for n = 1..300</a>
%H A086940 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (11,-10).
%F A086940 a(n) = 2*(10^n - 2).
%F A086940 R(a(n)) = A086945(n).
%F A086940 a(n) = 11*a(n-1) - 10*a(n-2); a(1)=16, a(2)=196. - _Harvey P. Dale_, Aug 11 2012
%F A086940 From _Elmo R. Oliveira_, Apr 30 2025: (Start)
%F A086940 G.f.: 4*x*(5*x+4)/((x-1)*(10*x-1)).
%F A086940 E.g.f.: 2*(1 - 2*exp(x) + exp(10*x)).
%F A086940 a(n) = 4*A198971(n-1) = A086942(n)/2. (End)
%t A086940 Table[FromDigits[Join[PadRight[{1},n,9],{6}]],{n,20}] (* or *) 2 (10^Range[20] - 2) (* or *) LinearRecurrence[{11,-10},{16,196},20] (* _Harvey P. Dale_, Aug 11 2012 *)
%o A086940 (Magma) [2*(10^n-2): n in [1..20] ]; // _Vincenzo Librandi_, Aug 22 2011
%Y A086940 Cf. A004086, A086942, A086945, A198971.
%K A086940 nonn,base,easy
%O A086940 1,1
%A A086940 _Ray Chandler_, Jul 24 2003