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%I #11 Sep 08 2022 08:46:00
%S 3,18,123,858,6003,42018,294123,2058858,14412003,100884018,706188123,
%T 4943316858,34603218003,242222526018,1695557682123,11868903774858,
%U 83082326424003,581576284968018,4071033994776123,28497237963432858
%N (5*7^n+1)/2.
%H Vincenzo Librandi, <a href="/A199421/b199421.txt">Table of n, a(n) for n = 0..1000</a>
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (8,-7).
%F a(n) = 7*a(n-1)-3.
%F a(n) = 8*a(n-1)-7*a(n-2).
%F G.f.: 3*(1-2*x)/((1-x)*(1-7*x)).
%o (Magma) [(5*7^n+1)/2: n in [0..30]];
%K nonn,easy
%O 0,1
%A _Vincenzo Librandi_, Nov 07 2011