A198480 a(n) = 2*7^n - 1.
1, 13, 97, 685, 4801, 33613, 235297, 1647085, 11529601, 80707213, 564950497, 3954653485, 27682574401, 193778020813, 1356446145697, 9495123019885, 66465861139201, 465261027974413, 3256827195820897, 22797790370746285
Offset: 0
Links
- Vincenzo Librandi, Table of n, a(n) for n = 0..1000
- Index entries for linear recurrences with constant coefficients, signature (8,-7).
Programs
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Magma
[2*7^n-1: n in [0..20]]
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Mathematica
CoefficientList[Series[(1+5*x)/((1-x)*(1-7*x)),{x,0,40}],x] (* Vincenzo Librandi, Jul 06 2012 *) 2*7^Range[0,20]-1 (* or *) LinearRecurrence[{8,-7},{1,13},20] (* Harvey P. Dale, Aug 19 2022 *) -
Maxima
A198480(n):=2*7^n-1$ makelist(A198480(n),n,0,20); /* Martin Ettl, Nov 09 2012 */
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PARI
a(n)=2*7^n-1 \\ Charles R Greathouse IV, Dec 28 2011
Formula
a(n) = 7*a(n-1)+6, n>0.
G.f.: (1+5*x)/((1-x)*(1-7*x)). - Vincenzo Librandi, Jul 06 2012
a(n) = 8*a(n-1) -7*a(n-2). - Vincenzo Librandi, Jul 06 2012