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A198970
a(n) = 4*10^n - 1.
1
3, 39, 399, 3999, 39999, 399999, 3999999, 39999999, 399999999, 3999999999, 39999999999, 399999999999, 3999999999999, 39999999999999, 399999999999999, 3999999999999999, 39999999999999999, 399999999999999999, 3999999999999999999, 39999999999999999999, 399999999999999999999
OFFSET
0,1
FORMULA
a(n) = 3*A097166(n).
a(n) = 10*a(n-1) + 9, n > 0.
a(n) = 11*a(n-1) - 10*a(n-2), n > 1.
G.f.: 3*(1 + 2*x)/(1 - 11*x + 10*x^2). - Vincenzo Librandi, Jan 03 2013
E.g.f.: exp(x)*(4*exp(9*x) - 1). - Elmo R. Oliveira, Sep 10 2024
MATHEMATICA
CoefficientList[Series[3*(1 + 2*x)/(1 - 11*x + 10*x^2), {x, 0, 30}], x] (* Vincenzo Librandi, Jan 03 2013 *)
PROG
(Magma) [4*10^n-1 : n in [0..20]];
CROSSREFS
Cf. A097166.
Sequence in context: A191468 A203243 A063035 * A361539 A014850 A341671
KEYWORD
nonn,easy
AUTHOR
Vincenzo Librandi, Nov 01 2011
STATUS
approved