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 A003606 a(n) = number of types of conjugacy classes in GL(n,q) (this is independent of q). (Formerly M3340) 2
 1, 4, 8, 22, 42, 103, 199, 441, 859, 1784, 3435, 6882, 13067, 25366, 47623, 90312, 167344, 311603, 570496, 1045896, 1893886, 3426466, 6140824, 10984249, 19499214, 34526844, 60758733, 106613119, 186099976, 323883380, 561141244, 969308408 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 REFERENCES 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=1..500 J. A. Green, The characters of the finite general linear groups, Trans. Amer. Math. Soc., 80 (1955), 402-447. N. J. A. Sloane, Transforms R. Steinberg, A geometric approach to the representations of the full linear group over a Galois field, Trans. Amer. Math. Soc., 71 (1951), 274-282. FORMULA G.f.: Product_{k >= 1} f(x^k)^p_k, where f(x)=Product_{k >= 0} 1/(1-x^k) = Sum_{k >= 0} p_k*x^k and p_k is the number of partitions of k (A000041). Recurrence relation: a(n+1) = 1/(n+1) * Sum_{k=0..n} a(k)*g(n-k+1) where g(n) = Sum_{ij | n} p(i)*i*j, with the sum over all ordered pairs (i, j) such that their products divide n and p(i) is the number of partitions of i. Also a(0)=1. - Brett Witty (witty(AT)maths.anu.edu.au), Jul 17 2003 Euler transform of A047968(n). - Vladeta Jovovic, Jun 23 2004 Recurrence relation: a(0)=1, a(n+1) = 1/(n+1) * Sum_{k=0..n} a(k)*g(n-k+1) where g(n) = Sum_{d | n} d * A000041(d) * A000203(n/d). - Brett Witty (witty(AT)maths.anu.edu.au), Jul 12 2006 EXAMPLE a(2) = 4 as there are four types of conjugacy classes of 2 X 2 matrices over GF(q): * the scalar matrices (diagonal matrix with both entries the same) * the direct sum of two scalars (diagonal matrix with both entries different) * the non-diagonalizable Jordan block (upper triangular matrix with the same entry along the diagonal and a 1 in the superdiagonal) * companion matrices of irreducible quadratics over GF(q) This example can be found in Green's paper (in the references). MATHEMATICA m = 32; f[x_] = Product[1/(1-x^k), {k, 1, m}]; gf[x_] = Product[f[x^k]^PartitionsP[k], {k, 1, m}]; Drop[ CoefficientList[ Series[gf[x], {x, 0, m}], x], 1] (* Jean-François Alcover, Aug 01 2011, after g.f. *) PROG (GAP) a := function(n) local k, sum; sum := 0; for k in [0..n-1] do sum := sum + a(k)*g(n-k); od; return sum/n; end; g := function(n) local i, j, sum; for i in DivisorsInt(n) do for j in DivisorsInt(n/i) do sum := sum + NrPartitions(i)*i*j; od; od; return sum; end;; # This code is significantly faster if you store previously computed values of a(n) and g(n). # Brett Witty (witty(AT)maths.anu.edu.au), Jul 17 2003 (GAP) a := function(n) if( n = 0) then return 1; else return Sum([0..n], i -> t(i) * Sum(DivisorsInt(n-i), d -> d * NrPartitions(d) * Sigma(n/d)) )/n; fi; end;; # Brett Witty (witty(AT)maths.anu.edu.au), Jul 12 2006 CROSSREFS Cf. A001970. Cf. A006951, A006952, A049314, A049315, A049316. Sequence in context: A332199 A200149 A153765 * A048657 A322284 A175655 Adjacent sequences:  A003603 A003604 A003605 * A003607 A003608 A003609 KEYWORD nonn,nice,easy AUTHOR EXTENSIONS More terms from Brett Witty (witty(AT)maths.anu.edu.au), Jul 17 2003 STATUS approved

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Last modified April 12 21:13 EDT 2021. Contains 342932 sequences. (Running on oeis4.)