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A055010
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a(0) = 0; for n > 0, 3*2^(n-1) - 1.
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27
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0, 2, 5, 11, 23, 47, 95, 191, 383, 767, 1535, 3071, 6143, 12287, 24575, 49151, 98303, 196607, 393215, 786431, 1572863, 3145727, 6291455, 12582911, 25165823, 50331647, 100663295, 201326591, 402653183, 805306367, 1610612735
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OFFSET
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0,2
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COMMENTS
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Apart from leading term (which should really be 3/2), same as A083329.
Written in binary, a(n) is 1011111...1
The sequence 2,5,11,23,47,95,... apparently gives values of n such that Nim-factorial(n) = 2. Cf. A059970. However, compare A060152. More work is needed! - John W. Layman, Mar 09 2001
With offset 1, number of (132,3412)-avoiding two-stack sortable permutations.
Number of descents after n+1 iterations of morphism A007413.
a(n) = A164874(n,1), n>0; subsequence of A030130. [From Reinhard Zumkeller, Aug 29 2009]
Let A be the Hessenberg matrix of order n, defined by: A[1,j]=[i,i]:=1, A[i,i-1]=-1, and A[i,j]=0 otherwise. Then, for n>=1, a(n-1)=(-1)^n*charpoly(A,-1). [From Milan Janjic, Jan 24 2010]
a(n+1) = A196168(A000079(n)). [Reinhard Zumkeller, Oct 28 2011]
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LINKS
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Vincenzo Librandi, Table of n, a(n) for n = 0..1000
Eric Weisstein's World of Mathematics, Thabit ibn Kurrah Number
E. S. Egge and T. Mansour, 132-avoiding two-stack sortable permutations..., arXiv:math.CO/0205206
S. Kitaev and T. Mansour, Counting the occurrences of generalized patterns..., arXiv:math.CO/0210170
Index to sequences with linear recurrences with constant coefficients, signature (3,-2).
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FORMULA
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a(n) = 2*a(n-1) + 1 = a(n-1) + A007283(n-1) = A007283(n)-1 = A000079(n) + A000225(n + 1) = A000079(n + 1) + A000225(n) = 3*A000079(n)-1 = 3*A000225(n) + 2.
a(n) = A010036(n)/2^(n-1) . - Philippe Deléham, Feb 20 2004
a(n) = A099258(A033484(n)-1) = floor(A033484(n)/2). - Reinhard Zumkeller, Oct 09 2004
a(n)=[ -1+3*2^(n-1)]*{1-[C(2*n,n) mod 2]}, with n>=0 [From Paolo P. Lava, Nov 20 2008]
G.f.: x*(2-x)/((1-x)*(1-2*x)). [From Philippe Deléham, Oct 04 2011]
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EXAMPLE
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a(3) = 3*2^2-1 = 3*4-1 = 11
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MATHEMATICA
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a=2; lst={0, a}; k=3; Do[a+=k; AppendTo[lst, a]; k+=k, {n, 0, 6!}]; lst [From Vladimir Joseph Stephan Orlovsky, Dec 15 2008]
Join[{0}, 3*2^Range[0, 30]-1] (* Harvey P. Dale, May 05 2013 *)
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PROG
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(MAGMA) [Floor(3*2^(n-1) - 1): n in [0..35]]; // Vincenzo Librandi, May 18 2011
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CROSSREFS
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Cf. A007505 for primes in this sequence. Apart from initial term, same as A052940 and A083329.
a(n) = A118654(n-1, 4), for n > 0.
Sequence in context: A133489 A060153 A086219 * A083329 A153893 A081973
Adjacent sequences: A055007 A055008 A055009 * A055011 A055012 A055013
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KEYWORD
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easy,nonn
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AUTHOR
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Henry Bottomley, May 31 2000
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STATUS
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approved
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