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 A086224 a(n) = 7*2^n-1. 17
 6, 13, 27, 55, 111, 223, 447, 895, 1791, 3583, 7167, 14335, 28671, 57343, 114687, 229375, 458751, 917503, 1835007, 3670015, 7340031, 14680063, 29360127, 58720255, 117440511, 234881023, 469762047, 939524095, 1879048191, 3758096383 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS a(n) = A164874(n+2,2); subsequence of A030130. - Reinhard Zumkeller, Aug 29 2009 Let A be the Hessenberg matrix of order n, defined by: A[1,j]=1, A[i,i]:=-3, A[i,i-1]=-1, and A[i,j]=0 otherwise. Then, for n>=1, a(n-1)=(-1)^n*charpoly(A,-5). - Milan Janjic, Jan 27 2010 LINKS Index entries for linear recurrences with constant coefficients, signature (3,-2). FORMULA a(n+1) = 2*a(n) + 1. G.f.: (6-5*x)/((1-x)*(1-2*x)) - Jaume Oliver Lafont, Sep 14 2009 a(n-1)^2 + a(n) = (7*2^(n-1))^2. - Vincenzo Librandi, Aug 08 2010 MATHEMATICA a=6; lst={a}; k=7; Do[a+=k; AppendTo[lst, a]; k+=k, {n, 0, 5!}]; lst (* Vladimir Joseph Stephan Orlovsky, Dec 16 2008 *) 7*2^Range[0, 30]-1 (* Harvey P. Dale, May 09 2018 *) PROG (PARI) a(n)=7<

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Last modified August 5 15:48 EDT 2020. Contains 336213 sequences. (Running on oeis4.)