

A005329


a(n) = Product_{i=1..n}(2^i  1). Also called 2factorial numbers.
(Formerly M3085)


46



1, 1, 3, 21, 315, 9765, 615195, 78129765, 19923090075, 10180699028325, 10414855105976475, 21319208401933844325, 87302158405919092510875, 715091979502883286756577125, 11715351900195736886933003038875
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OFFSET

0,3


COMMENTS

Conjecture: this sequence is the inverse binomial transform of A075272 or, equivalently, the inverse binomial transform of the BinomialMean transform of A075271.  John W. Layman, Sep 12 2002
To win a game, you must flip n+1 heads in a row, where n is the total number of tails flipped so far. Then the probability of winning for the first time after n tails is A005329 / A006125. The probability of having won before n+1 tails is A114604 / A006125.  Joshua Zucker, Dec 14 2005
Number of upper triangular n X n (0,1)matrices with no zero rows.  Vladeta Jovovic, Mar 10 2008
Equals the qFibonacci series for q = (2), and the series prefaced with a 1: (1, 1, 1, 3, 21, ...) dot (1, 2, 4, 8, ...) if n is even, and (1, 2, 4, 8, ...) if n is odd. For example, a(3) = 21 = (1, 1, 1, 3) dot (1, 2, 4, 8) = (1, 2, 4, 24) and a(4) = 315 = (1, 1, 1, 3, 21) dot (1, 2, 4, 8 16) = (1, 2, 4, 24, 336).  Gary W. Adamson, Apr 17 2009
Number of chambers in an A_n(K) building where K=GF(2) is the field of two elements. This is also the number of maximal flags in a ndimensional vector space over a field of two elements.  Marcos Spreafico, Mar 22 2012
Given probability p = 1/2^n that an outcome will occur at the nth stage of an infinite process, then starting at n=1, A114604(n)/A006125(n+2) = 1a(n)/A006125(n+1) is the probability that the outcome has occurred up to and including the nth iteration. The limiting ratio is 1A048651 ~ 0.7112119. These observations are a more formal and generalized statement of Joshua Zucker's Dec 14, 2005 comment.  Bob Selcoe, Mar 02 2016
Also the number of dominating sets in the ntriangular honeycomb rook graph.  Eric W. Weisstein, Jul 14 2017


REFERENCES

M. Ronan, Lectures on Buildings (Perspectives in Mathematics; Vol. 7), Academic Press Inc., 1989.
N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).


LINKS

T. D. Noe, Table of n, a(n) for n = 0..50
E. Andresen, K. Kjeldsen, On certain subgraphs of a complete transitively directed graph, Discrete Math. 14 (1976), no. 2, 103119.
Kent E. Morrison, Integer Sequences and Matrices Over Finite Fields, Journal of Integer Sequences, Vol. 9 (2006), Article 06.2.1.
Eric Weisstein's World of Mathematics, Dominating Set
Eric Weisstein's World of Mathematics, qFactorial
Index entries for sequences related to factorial numbers


FORMULA

a(n)/2^(n*(n+1)/2) > c = 0.2887880950866024212788997219294585937270... (see A048651, A048652).
From Paul D. Hanna, Sep 17 2009: (Start)
G.f.: Sum_{n>=0} 2^(n*(n+1)/2) * x^n / (Product_{k=0..n} (1+2^k*x)).
Compare to: 1 = Sum_{n>=0} 2^(n*(n+1)/2) * x^n/(Product_{k=1..n+1} (1+2^k*x)). (End)
G.f. satisfies: A(x) = 1 + Sum_{n>=1} x^n/n! * d^n/dx^n x*A(x).  Paul D. Hanna, Apr 21 2012
a(n) = 2^(binomial(n+1,2))*(1/2; 1/2)_{n}, where (a;q)_{n} is the qPochhammer symbol.  G. C. Greubel, Dec 23 2015
a(n) = Product_{i=1..n} A000225(i).  Michel Marcus, Dec 27 2015


MAPLE

A005329 := proc(n) option remember; if n<=1 then 1 else (2^n1)*A005329(n1); fi; end;


MATHEMATICA

a[0] = 1; a[n_] := a[n] = (2^n1)*a[n1]; a /@ Range[0, 14] (* JeanFrançois Alcover, Apr 22 2011 *)
FoldList[Times, 1, 2^Range[15]  1] (* Harvey P. Dale, Dec 21 2011 *)
Table[QFactorial[n, 2], {n, 0, 14}] (* Arkadiusz Wesolowski, Oct 30 2012 *)
QFactorial[Range[0, 10], 2] (* Eric W. Weisstein, Jul 14 2017 *)


PROG

(PARI) a(n)=polcoeff(sum(m=0, n, 2^(m*(m+1)/2)*x^m/prod(k=0, m, 1+2^k*x+x*O(x^n))), n) \\ Paul D. Hanna, Sep 17 2009
(PARI) Dx(n, F)=local(D=F); for(i=1, n, D=deriv(D)); D
a(n)=local(A=1+x+x*O(x^n)); for(i=1, n, A=1+sum(k=1, n, x^k/k!*Dx(k, x*A+x*O(x^n) ))); polcoeff(A, n) \\ Paul D. Hanna, Apr 21 2012
(MAGMA) [1] cat [&*[ 2^k1: k in [1..n] ]: n in [1..16]]; // Vincenzo Librandi, Dec 24 2015


CROSSREFS

Cf. A000225, A005321, A005329, A006125, A114604, A006088, A028362, A027871, A027872, A027873, A048651, A048652, A075271, A075272.
Sequence in context: A055555 A208731 A158888 * A134528 A118410 A125054
Adjacent sequences: A005326 A005327 A005328 * A005330 A005331 A005332


KEYWORD

nonn,easy,nice,changed


AUTHOR

N. J. A. Sloane


EXTENSIONS

More terms from Olivier Gérard, Aug 1997
Better definition from Leslie Ann Goldberg (leslie(AT)dcs.warwick.ac.uk), Dec 11 1999


STATUS

approved



