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121n - 1.
1

%I #20 Sep 08 2022 08:45:42

%S 120,241,362,483,604,725,846,967,1088,1209,1330,1451,1572,1693,1814,

%T 1935,2056,2177,2298,2419,2540,2661,2782,2903,3024,3145,3266,3387,

%U 3508,3629,3750,3871,3992,4113,4234,4355,4476,4597,4718,4839,4960,5081,5202

%N 121n - 1.

%H Vincenzo Librandi, <a href="/A158130/b158130.txt">Table of n, a(n) for n = 1..10000</a>

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (2,-1).

%F a(n) = 2*a(n-1) -a(n-2).

%F G.f.: x*(120+x)/(x-1)^2.

%t Table[121n-1,{n,50}]

%o (Magma) I:=[120, 241]; [n le 2 select I[n] else 2*Self(n-1)-Self(n-2): n in [1..50]];

%o (PARI) a(n) = 121*n - 1.

%K nonn,easy

%O 1,1

%A _Vincenzo Librandi_, Mar 13 2009