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 A034356 Triangle read by rows giving T(n,k) = number of inequivalent linear [n,k] binary codes (n >= 1, 1 <= k <= n). 23
 1, 2, 1, 3, 3, 1, 4, 6, 4, 1, 5, 10, 10, 5, 1, 6, 16, 22, 16, 6, 1, 7, 23, 43, 43, 23, 7, 1, 8, 32, 77, 106, 77, 32, 8, 1, 9, 43, 131, 240, 240, 131, 43, 9, 1, 10, 56, 213, 516, 705, 516, 213, 56, 10, 1, 11, 71, 333, 1060, 1988, 1988, 1060, 333, 71, 11, 1, 12, 89 (list; table; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS Harald Fripertinger, Isometry Classes of Codes. Harald Fripertinger, Wnk2: Number of the isometry classes of all binary (n,k)-codes. [This is a rectangular array whose lower triangle contains T(n,k).] H. Fripertinger and A. Kerber, Isometry classes of indecomposable linear codes, preprint, 1995. [We have T(n,k) = W_{nk2}; see p. 4 of the preprint.] H. Fripertinger and A. Kerber, Isometry classes of indecomposable linear codes. In: G. Cohen, M. Giusti, T. Mora (eds), Applied Algebra, Algebraic Algorithms and Error-Correcting Codes, 11th International Symposium, AAECC 1995, Lect. Notes Comp. Sci. 948 (1995), pp. 194-204. [We have T(n,k) = W_{nk2}; see p. 197.] Petros Hadjicostas, Generating function for column k=4. Petros Hadjicostas, Generating function for column k=5. Petros Hadjicostas, Generating function for column k=6. Kent E. Morrison, Integer Sequences and Matrices Over Finite Fields, Journal of Integer Sequences, Vol. 9 (2006), Article 06.2.1. David Slepian, Some further theory of group codes, Bell System Tech. J. 39(5) (1960), 1219-1252. David Slepian, Some further theory of group codes, Bell System Tech. J. 39(5) (1960), 1219-1252. Marcel Wild, Consequences of the Brylawski-Lucas Theorem for binary matroids, European Journal of Combinatorics 17 (1996), 309-316. Marcel Wild, The asymptotic number of inequivalent binary codes and nonisomorphic binary matroids, Finite Fields and their Applications 6 (2000), 192-202. Marcel Wild, The asymptotic number of binary codes and binary matroids, SIAM J. Discrete Math. 19(3) (2005), 691-699. [This paper apparently corrects errors in previous papers.] FORMULA From Petros Hadjicostas, Sep 30 2019: (Start) T(n,k) = Sum_{i = k..n} A034253(i,k) for 1 <= k <= n. G.f. for column k=1: x/(1-x)^2. G.f. for column k=2: -(x^3 - x - 1)*x^2/((x^2 + x + 1)*(x + 1)*(x - 1)^4). G.f. for column k=3: -(x^12 - 2*x^11 + x^10 - x^9 - x^6 + x^4 - x - 1)*x^3/((x^6 + x^5 + x^4 + x^3 + x^2 + x + 1)*(x^2 + x + 1)^2*(x^2 + 1)*(x + 1)^2*(x - 1)^8). G.f. for column k >= 4: modify the Sage program below (cf. function f). It is too complicated to write it here. For some cases, see also the links above. (End) EXAMPLE Table T(n,k) (with rows n >= 1 and columns k >= 1) begins as follows:   1;   2,  1;   3,  3,  1;   4,  6,  4,   1;   5, 10, 10,   5,  1;   6, 16, 22,  16,  6,  1;   7, 23, 43,  43, 23,  7, 1;   8, 32, 77, 106, 77, 32, 8, 1;   ... PROG (Sage) # Fripertinger's method to find the g.f. of column k >= 2 (for small k): def A034356col(k, length):     G1 = PSL(k, GF(2))     G2 = PSL(k-1, GF(2))     D1 = G1.cycle_index()     D2 = G2.cycle_index()     f1 = sum(i*prod(1/(1-x^j) for j in i) for i in D1)     f2 = sum(i*prod(1/(1-x^j) for j in i) for i in D2)     f = (f1 - f2)/(1-x)     return f.taylor(x, 0, length).list() # For instance the Taylor expansion for column k = 4 gives print(A034356col(4, 30)) # Petros Hadjicostas, Oct 07 2019 CROSSREFS This is A076831 with the k=0 column omitted. Columns include A000027 (k=1), A034198 (k=2), A034357 (k=3), A034358 (k=4), A034359 (k=5), A034360 (k=6), A034361 (k=7), A034362 (k=8). Cf. A034253, A034254, A034328. Sequence in context: A284855 A074909 A135278 * A075195 A293311 A126885 Adjacent sequences:  A034353 A034354 A034355 * A034357 A034358 A034359 KEYWORD tabl,nonn,changed AUTHOR STATUS approved

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Last modified October 18 07:19 EDT 2019. Contains 328146 sequences. (Running on oeis4.)