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 A122949 Number of ordered pairs of permutations generating a transitive group. 6
 1, 3, 26, 426, 11064, 413640, 20946960, 1377648720, 114078384000, 11611761920640, 1425189271161600, 207609729886944000, 35419018603306060800, 6996657393055480550400, 1584616114318716544665600, 407930516160959891683584000, 118458533875304716189544448000 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 COMMENTS From Dixon: The sequence is asymptotic to (n!)^2; when divided by n!^2, it has a high-order asymptotic contact with the probability that two randomly chosen permutations generate the symmetric group. Also: a(n)=(n-1)!*A003319(n+1), where A003319 is the number of connected [or indecomposable] permutations. The coefficients in the asymptotic expansion of a(n)/(n!)^2 are A113869 and in absolute value, they constitute A084357 (number of sets of sets of lists). LINKS Seiichi Manyama, Table of n, a(n) for n = 1..253 John D. Dixon, Asymptotics of Generating the Symmetric and Alternating Groups, Electronic Journal of Combinatorics, vol 11(2), R56. P. Flajolet and R. Sedgewick, Analytic Combinatorics, 2009; page 139. FORMULA Exponential generating function is: log(1+Sum_{n>=1}n!*z^n). a(n) = (n!)^2 - (n-1)! * Sum_{k=1..n-1} a(k) * (n-k)! / (k-1)!. - Ilya Gutkovskiy, Jul 10 2020 EXAMPLE a(2)=3 because there are 2!*2!=4 pairs of permutations, of which only [(1,1),(1,1)] does not generate a transitive group. MAPLE series(log(add(n!*z^n, n=0..Order+2)), z=0):seq(coeff(%, z, j)*j!, j=0..Order); MATHEMATICA max = 15; Drop[ CoefficientList[ Series[ Log[1 + Sum[n!*z^n, {n, 1, max}]], {z, 0, max}], z]* Range[0, max]!, 1](* Jean-François Alcover, Oct 05 2011 *) PROG (PARI) N=20; x='x+O('x^N); Vec(serlaplace(log(sum(k=0, N, k!*x^k)))) \\ Seiichi Manyama, Mar 01 2019 CROSSREFS Cf. A003319, A084357, A113869. Sequence in context: A305144 A206402 A300954 * A305113 A251664 A182958 Adjacent sequences: A122946 A122947 A122948 * A122950 A122951 A122952 KEYWORD nonn AUTHOR Philippe Flajolet, Oct 25 2006 EXTENSIONS More terms from Seiichi Manyama, Mar 01 2019 STATUS approved

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