A086940 a(n) = k where R(k+4) = 2.
16, 196, 1996, 19996, 199996, 1999996, 19999996, 199999996, 1999999996, 19999999996, 199999999996, 1999999999996, 19999999999996, 199999999999996, 1999999999999996, 19999999999999996, 199999999999999996, 1999999999999999996, 19999999999999999996
Offset: 1
Links
- Vincenzo Librandi, Table of n, a(n) for n = 1..300
- Index entries for linear recurrences with constant coefficients, signature (11,-10).
Programs
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Magma
[2*(10^n-2): n in [1..20] ]; // Vincenzo Librandi, Aug 22 2011
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Mathematica
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 *)
Formula
a(n) = 2*(10^n - 2).
R(a(n)) = A086945(n).
a(n) = 11*a(n-1) - 10*a(n-2); a(1)=16, a(2)=196. - Harvey P. Dale, Aug 11 2012
From Elmo R. Oliveira, Apr 30 2025: (Start)
G.f.: 4*x*(5*x+4)/((x-1)*(10*x-1)).
E.g.f.: 2*(1 - 2*exp(x) + exp(10*x)).