cp's OEIS Frontend

A005329 a(n) = Product_{i=1..n} (2^i - 1). Also called 2-factorial numbers.

%I A005329 M3085 #159 Feb 16 2025 08:32:28
%S A005329 1,1,3,21,315,9765,615195,78129765,19923090075,10180699028325,
%T A005329 10414855105976475,21319208401933844325,87302158405919092510875,
%U A005329 715091979502883286756577125,11715351900195736886933003038875,383876935713713710574133710574817125
%N A005329 a(n) = Product_{i=1..n} (2^i - 1). Also called 2-factorial numbers.
%C A005329 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
%C A005329 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
%C A005329 Number of upper triangular n X n (0,1)-matrices with no zero rows. - _Vladeta Jovovic_, Mar 10 2008
%C A005329 Equals the q-Fibonacci 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
%C A005329 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 an n-dimensional vector space over a field of two elements. - _Marcos Spreafico_, Mar 22 2012
%C A005329 Given probability p = 1/2^n that an outcome will occur at the n-th stage of an infinite process, then starting at n=1, A114604(n)/A006125(n+2) = 1-a(n)/A006125(n+1) is the probability that the outcome has occurred up to and including the n-th iteration. The limiting ratio is 1-A048651 ~ 0.7112119. These observations are a more formal and generalized statement of Joshua Zucker's Dec 14, 2005 comment. - _Bob Selcoe_, Mar 02 2016
%C A005329 Also the number of dominating sets in the n-triangular honeycomb rook graph. - _Eric W. Weisstein_, Jul 14 2017
%C A005329 Empirical: Letting Q denote the Hall-Littlewood Q basis of the symmetric functions over the field of fractions of the univariate polynomial ring in t over the field of rational numbers, and letting h denote the complete homogeneous basis, a(n) is equal to the absolute value of 2^A000292(n) times the coefficient of h_{1^(n*(n+1)/2)} in Q_{(n, n-1, ..., 1)} with t evaluated at 1/2. - _John M. Campbell_, Apr 30 2018
%C A005329 The series f(x) = Sum_{n>=0} x^(2^n-1)/a(n) satisfies f'(x) = f(x^2), f(0) = 1. - _Lucas Larsen_, Jan 05 2022
%D A005329 Annie Cuyt, Vigdis Brevik Petersen, Brigitte Verdonk, Haakon Waadeland, and William B. Jones, Handbook of continued fractions for special functions, Springer, New York, 2008. (see 19.2.1)
%D A005329 Steven R. Finch, Mathematical Constants, Cambridge University Press, 2003, p. 358.
%D A005329 Mark Ronan, Lectures on Buildings (Perspectives in Mathematics; Vol. 7), Academic Press Inc., 1989.
%D A005329 N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence).
%H A005329 T. D. Noe, <a href="/A005329/b005329.txt">Table of n, a(n) for n = 0..50</a>
%H A005329 E. Andresen and K. Kjeldsen, <a href="http://dx.doi.org/10.1016/0012-365X(76)90054-6">On certain subgraphs of a complete transitively directed graph</a>, Discrete Math., Vol. 14, No. 2 (1976), pp. 103-119.
%H A005329 Paul Barry, <a href="https://arxiv.org/abs/2104.01644">Centered polygon numbers, heptagons and nonagons, and the Robbins numbers</a>, arXiv:2104.01644 [math.CO], 2021.
%H A005329 Geoffrey Critzer, <a href="https://esirc.emporia.edu/handle/123456789/3595">Combinatorics of Vector Spaces over Finite Fields</a>, Master's thesis, Emporia State University, 2018.
%H A005329 Hsien-Kuei Hwang, Emma Yu Jin, and Michael J. Schlosser, <a href="https://arxiv.org/abs/2012.13570">Asymptotics and statistics on Fishburn Matrices: dimension distribution and a conjecture of Stoimenow</a>, arXiv:2012.13570 [math.CO], 2020.
%H A005329 Kent E. Morrison, <a href="http://www.cs.uwaterloo.ca/journals/JIS/VOL9/Morrison/morrison37.html">Integer Sequences and Matrices Over Finite Fields</a>, Journal of Integer Sequences, Vol. 9 (2006), Article 06.2.1.
%H A005329 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/DominatingSet.html">Dominating Set</a>.
%H A005329 Eric Weisstein's World of Mathematics, <a href="https://mathworld.wolfram.com/q-Factorial.html">q-Factorial</a>.
%H A005329 <a href="/index/Fa#factorial">Index entries for sequences related to factorial numbers</a>.
%F A005329 a(n)/2^(n*(n+1)/2) -> c = 0.2887880950866024212788997219294585937270... (see A048651, A048652).
%F A005329 From _Paul D. Hanna_, Sep 17 2009: (Start)
%F A005329 G.f.: Sum_{n>=0} 2^(n*(n+1)/2) * x^n / (Product_{k=0..n} (1+2^k*x)).
%F A005329 Compare to: 1 = Sum_{n>=0} 2^(n*(n+1)/2) * x^n/(Product_{k=1..n+1} (1+2^k*x)). (End)
%F A005329 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
%F A005329 a(n) = 2^(binomial(n+1,2))*(1/2; 1/2)_{n}, where (a;q)_{n} is the q-Pochhammer symbol. - _G. C. Greubel_, Dec 23 2015
%F A005329 a(n) = Product_{i=1..n} A000225(i). - _Michel Marcus_, Dec 27 2015
%F A005329 From _Peter Bala_, Nov 10 2017: (Start)
%F A005329 O.g.f. as a continued fraction of Stieltjes' type: A(x) = 1/(1 - x/(1 - 2*x/(1 - 6*x/(1 - 12*x/(1 - 28*x/(1 - 56*x/(1 - ... -(2^n - 2^floor(n/2))*x/(1 - ... )))))))) (follows from Heine's continued fraction for the ratio of two q-hypergeometric series at q = 2. See Cuyt et al. 19.2.1).
%F A005329 A(x) = 1/(1 + x - 2*x/(1 - (2 - 1)^2*x/(1 + x - 2^3*x/(1 - (2^2 - 1)^2*x/(1 + x - 2^5*x/(1 - (2^3 - 1)^2*x/(1 + x - 2^7*x/(1 - (2^4 - 1)^2*x/(1 + x - ... ))))))))). (End)
%F A005329 0 = a(n)*(a(n+1) - a(n+2)) + 2*a(n+1)^2 for all n>=0. - _Michael Somos_, Feb 23 2019
%F A005329 From _Amiram Eldar_, Feb 19 2022: (Start)
%F A005329 Sum_{n>=0} 1/a(n) = A079555.
%F A005329 Sum_{n>=0} (-1)^n/a(n) = A048651. (End)
%e A005329 G.f. = 1 + x + 3*x^2 + 21*x^3 + 315*x^4 + 9765*x^5 + 615195*x^6 + 78129765*x^7 + ...
%p A005329 A005329 := proc(n) option remember; if n<=1 then 1 else (2^n-1)*procname(n-1); end if; end proc: seq(A005329(n), n=0..15);
%t A005329 a[0] = 1; a[n_] := a[n] = (2^n-1)*a[n-1]; a /@ Range[0,14] (* _Jean-François Alcover_, Apr 22 2011 *)
%t A005329 FoldList[Times, 1, 2^Range[15] - 1] (* _Harvey P. Dale_, Dec 21 2011 *)
%t A005329 Table[QFactorial[n, 2], {n, 0, 14}] (* _Arkadiusz Wesolowski_, Oct 30 2012 *)
%t A005329 QFactorial[Range[0, 10], 2] (* _Eric W. Weisstein_, Jul 14 2017 *)
%t A005329 a[ n_] := If[ n < 0, 0, (-1)^n QPochhammer[ 2, 2, n]]; (* _Michael Somos_, Jan 28 2018 *)
%o A005329 (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
%o A005329 (PARI) Dx(n,F)=local(D=F);for(i=1,n,D=deriv(D));D
%o A005329 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
%o A005329 (PARI) {a(n) = if( n<0, 0, prod(k=1, n, 2^k - 1))}; /* _Michael Somos_, Jan 28 2018 */
%o A005329 (PARI) {a(n) = if( n<0, 0, (-1)^n * sum(k=0, n+1, (-1)^k * 2^(k*(k+1)/2) * prod(j=1, k, (2^(n+1-j) - 1) / (2^j - 1))))}; /* _Michael Somos_, Jan 28 2018 */
%o A005329 (Magma) [1] cat [&*[ 2^k-1: k in [1..n] ]: n in [1..16]]; // _Vincenzo Librandi_, Dec 24 2015
%o A005329 (GAP) List([0..15],n->Product([1..n],i->2^i-1)); # _Muniru A Asiru_, May 18 2018
%Y A005329 Cf. A000225, A005321, A006125, A114604, A006088, A028362, A027871 (3-fac), A027872 (5-fac), A027873 (6-fac), A048651, A048652, A075271, A075272, A032085, A122746.
%Y A005329 Cf. A048651, A079555, A152476 (inverse binomial transform).
%Y A005329 Column q=2 of A069777.
%K A005329 nonn,easy,nice
%O A005329 0,3
%A A005329 _N. J. A. Sloane_
%E A005329 Better definition from Leslie Ann Goldberg (leslie(AT)dcs.warwick.ac.uk), Dec 11 1999