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 A006116 Sum of Gaussian binomial coefficients [n,k] for q=2 and k=0..n. (Formerly M1501) 22
 1, 2, 5, 16, 67, 374, 2825, 29212, 417199, 8283458, 229755605, 8933488744, 488176700923, 37558989808526, 4073773336877345, 623476476706836148, 134732283882873635911, 41128995468748254231002, 17741753171749626840952685, 10817161765507572862559462656 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Also number of distinct binary linear codes of length n and any dimension. Equivalently, number of subgroups of the Abelian group (C_2)^n. The subsequence of primes in this sum of Gaussian binomial coefficients begins: 2, 5, 67, no more through a(19). [Jonathan Vos Post, Mar 11 2010] Let V_n be an n-dimensional vector space over a field with 2 elements. Let P(V_n) be the collection of all subspaces of V_n. Then a(n-1) is the number of times any given nonzero vector of V_n appears in P(V_n). - Geoffrey Critzer, Jun 05 2017 REFERENCES J. Goldman and G.-C. Rota, The number of subspaces of a vector space, pp. 75-83 of W. T. Tutte, editor, Recent Progress in Combinatorics. Academic Press, NY, 1969. I. P. Goulden and D. M. Jackson, Combinatorial Enumeration. Wiley, NY, 1983, p, 99. F. J. MacWilliams and N. J. A. Sloane, The Theory of Error-Correcting Codes, Elsevier-North Holland, 1978, p. 698. N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..100 S. Hitzemann, W. Hochstattler, On the combinatorics of Galois numbers, Discr. Math. 310 (2010) 3551-3557, Galois Numbers G_{n}^(2). Kent E. Morrison, Integer Sequences and Matrices Over Finite Fields, Journal of Integer Sequences, Vol. 9 (2006), Article 06.2.1. D. Slepian, A class of binary signaling alphabets, Bell System Tech. J. 35 (1956), 203-234. D. Slepian, Some further theory of group codes, Bell System Tech. J. 39 1960 1219-1252. M. Sved, Gaussians and binomials, Ars. Combinatoria, 17A (1984), 325-351. (Annotated scanned copy) FORMULA O.g.f.: A(x) = Sum_{n>=0} x^n / Product_{k=0..n} (1 - 2^k*x). - Paul D. Hanna, Dec 06 2007 From Paul D. Hanna, Nov 29 2008: (Start) Coefficients of the square of the q-exponential of x evaluated at q=2, where the q-exponential of x = Sum_{n>=0} x^n/F(n) and F(n) = Product{i=1..n} (q^i-1)/(q-1) is the q-factorial of n. G.f.: [Sum_{k=0..n} x^n/F(n)]^2 = Sum_{k=0..n} a(n)*x^n/F(n) where F(n)=A005329(n)=Product{i=1..n}(2^i - 1). a(n) = Sum_{k=0..n} F(n)/(F(k)*F(n-k)) where F(n)=A005329(n) is the 2-factorial of n. a(n) = Sum_{k=0..n} Product_{i=1..n-k} (2^(i+k) - 1)/(2^i - 1). a(n) = Sum_{k=0..A033638(n)} A083906(n,k)*2^k. (End) G.f.: 1 + x*(G(0) - 1)/(x-1) where G(k) =  1 - 1/(1-2^k*x)/(1-x/(x-1/G(k+1) )); (recursively defined continued fraction). - Sergei N. Gladkovskii, Jan 16 2013 a(n) = 2*a(n-1)+(2^(n-1)-1)*a(n-2). [Hitzemann and Hochstattler]. - R. J. Mathar, Aug 21 2013 a(n) ~ c * 2^(n^2/4), where c = EllipticTheta[3,0,1/2] / QPochhammer[1/2,1/2] = 7.3719688014613... if n is even and c = EllipticTheta[2,0,1/2] / QPochhammer[1/2,1/2] = 7.3719494907662... if n is odd. - Vaclav Kotesovec, Aug 21 2013 EXAMPLE O.g.f.: A(x) = 1/(1-x) + x/((1-x)*(1-2x)) + x^2/((1-x)*(1-2x)*(1-4x)) + x^3/((1-x)*(1-2x)*(1-4x)*(1-8x)) + ... Also generated by iterated binomial transforms in the following way: [1,2,5,16,67,374,2825,29212,...] = BINOMIAL([1,1,2,6,26,158,1330,..]); see A135922; [1,2,6,26,158,1330,15414,245578,...] = BINOMIAL([1,1,3,13,83,749,...]); [1,3,13,83,749,9363,160877,...] = BINOMIAL^2([1,1,5,33,317,4361,...]); [1,5,33,317,4361,82789,2148561,...] = BINOMIAL^4([1,1,9,97,1433,...]); [1,9,97,1433,30545,902601,...] = BINOMIAL^8([1,1,17,321,7601,252833,...]); etc. MAPLE gf:= m-> add(x^n/mul(1-2^k*x, k=0..n), n=0..m): a:= n-> coeff(series(gf(n), x, n+1), x, n): seq(a(n), n=0..20);  # Alois P. Heinz, Apr 24 2012 MATHEMATICA faq[n_, q_] = Product[(1-q^(1+k))/(1-q), {k, 0, n-1}]; qbin[n_, m_, q_] = faq[n, q]/(faq[m, q]*faq[n-m, q]); a[n_] := Sum[qbin[n, k, 2], {k, 0, n}]; a /@ Range[0, 19] (* Jean-François Alcover, Jul 21 2011 *) Flatten[{1, RecurrenceTable[{a[n]==2*a[n-1]+(2^(n-1)-1)*a[n-2], a[0]==1, a[1]==2}, a, {n, 1, 15}]}] (* Vaclav Kotesovec, Aug 21 2013 *) QP = QPochhammer; a[n_] := Sum[QP[2, 2, n]/(QP[2, 2, k]*QP[2, 2, n-k]), {k, 0, n}]; Table[a[n], {n, 0, 20}] (* Jean-François Alcover, Nov 23 2015 *) Table[Sum[QBinomial[n, k, 2], {k, 0, n}], {n, 0, 19}] (* Ivan Neretin, Mar 28 2016 *) PROG (PARI) a(n)=polcoeff(sum(k=0, n, x^k/prod(j=0, k, 1-2^j*x+x*O(x^n))), n) \\ Paul D. Hanna, Dec 06 2007 (PARI) a(n, q=2)=sum(k=0, n, prod(i=1, n-k, (q^(i+k)-1)/(q^i-1))) \\ Paul D. Hanna, Nov 29 2008 (MAGMA) I:=[1, 2]; [n le 2 select I[n] else 2*Self(n-1)+(2^(n-2)-1)*Self(n-2): n in [1..20]]; // Vincenzo Librandi, Aug 12 2014 CROSSREFS Cf. A006516. Row sums of A022166. Cf. A005329, A083906. - Paul D. Hanna, Nov 29 2008 Sequence in context: A239911 A275518 A005163 * A122082 A002631 A107948 Adjacent sequences:  A006113 A006114 A006115 * A006117 A006118 A006119 KEYWORD nonn,easy,nice AUTHOR STATUS approved

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Last modified November 18 05:08 EST 2017. Contains 294853 sequences.