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a(n) = 10*2^(n-1) - 9.
10

%I #45 Dec 29 2023 10:08:56

%S 1,11,31,71,151,311,631,1271,2551,5111,10231,20471,40951,81911,163831,

%T 327671,655351,1310711,2621431,5242871,10485751,20971511,41943031,

%U 83886071,167772151,335544311,671088631,1342177271,2684354551

%N a(n) = 10*2^(n-1) - 9.

%C Binomial transform of [1, 10, 10, 10,...].

%C A007318 * [1, 10, 10, 10,...].

%C The binomial transform of [1, c, c, c,...] has the terms a(n)=1-c+c*2^(n-1) if the offset 1 is chosen. The o.g.f. of the a(n) is x{1+(c-2)x}/{(2x-1)(x-1)}. This applies to A139634 with c=10, to A139635 with c=11, to A139697 with c=12, to A139698 with c=25 and to A099003, A139700, A139701 accordingly. - _R. J. Mathar_, May 11 2008

%H Vincenzo Librandi, <a href="/A139634/b139634.txt">Table of n, a(n) for n = 1..1000</a>

%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (3,-2).

%F a(n) = 2*a(n-1) + 9, with n>1, a(1)=1. - _Vincenzo Librandi_, Nov 24 2010

%F From _Colin Barker_, Oct 10 2013: (Start)

%F a(n) = 3*a(n-1) - 2*a(n-2).

%F G.f.: x*(8*x+1) / ((x-1)*(2*x-1)). (End)

%e a(4) = 71 = (1, 3, 3, 1) dot (1, 10, 10, 10) = (1 + 30 + 30 + 10).

%p A139634:=n->10*2^(n-1)-9; seq(A139634(n), n=1..30); # _Wesley Ivan Hurt_, Mar 26 2014

%t a=1; lst={a}; k=10; Do[a+=k; AppendTo[lst, a]; k+=k, {n, 0, 5!}]; lst (* _Vladimir Joseph Stephan Orlovsky_, Dec 17 2008 *)

%t CoefficientList[Series[(8 x + 1)/((x - 1) (2 x - 1)), {x, 0, 50}], x] (* _Vincenzo Librandi_, Mar 30 2014 *)

%t LinearRecurrence[{3,-2},{1,11},30] (* _Harvey P. Dale_, Feb 19 2023 *)

%o (Magma) [10*2^(n-1)-9: n in [1..50]]; // _Vincenzo Librandi_, Mar 30 2014

%o (PARI) a(n)=10*2^(n-1)-9 \\ _Charles R Greathouse IV_, Oct 07 2015

%Y Cf. A007318.

%K nonn,easy

%O 1,2

%A _Gary W. Adamson_, Apr 29 2008

%E More terms from _Vladimir Joseph Stephan Orlovsky_, Dec 17 2008

%E Simpler definition from _Jon E. Schoenfield_, Jun 23 2010