A131970 - OEIS

%I #24 Mar 11 2024 01:44:02

%S 1,122,12222,1222222,122222222,12222222222,1222222222222,

%T 122222222222222,12222222222222222,1222222222222222222,

%U 122222222222222222222,12222222222222222222222

%N 1 followed by 2n 2's.

%H Vincenzo Librandi, <a href="/A131970/b131970.txt">Table of n, a(n) for n = 0..200</a>

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (101, -100).

%F From _Chai Wah Wu_, Jun 17 2020: (Start)

%F a(n) = 101*a(n-1) - 100*a(n-2) for n > 1.

%F G.f.: (21*x + 1)/((x - 1)*(100*x - 1)). (End)

%t NestList[FromDigits[PadRight[IntegerDigits[#],IntegerLength[#]+2,2]]&,1,20]  (* _Harvey P. Dale_, Mar 06 2011 *)

%t Table[FromDigits[PadRight[{1},2n+1,2]],{n,0,20}] (* _Harvey P. Dale_, Jul 30 2020 *)

%o (Magma) [2*(10^(2*n)-1)/9+10^(2*n): n in [0..15]]; // _Vincenzo Librandi_, Aug 10 2011

%K nonn,base,easy

%O 0,2

%A _Paul Curtz_, Oct 06 2007