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 A085584 Number of (3412,2341)-, (3412,4123)- and (3412,52341)-avoiding involutions in S_n. 0
 1, 2, 4, 9, 20, 45, 100, 222, 491, 1086, 2401, 5310, 11744, 25977, 57460, 127101, 281144, 621882, 1375579, 3042726, 6730385, 14887338, 32930188, 72840249, 161119700, 356390301, 788321020, 1743734406, 3857070395, 8531684622 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,2 LINKS FORMULA G.f. (1-x^2)*(1-x)^2/(1-3*x+x^2+3*x^3-3*x^4). MATHEMATICA CoefficientList[Series[(1-x^2)(1-x)^2/(1-3x+x^2+3x^3-3x^4), {x, 0, 40}], x] (* Harvey P. Dale, May 28 2017 *) CROSSREFS Sequence in context: A091620 A208738 A108469 * A080019 A052534 A213411 Adjacent sequences:  A085581 A085582 A085583 * A085585 A085586 A085587 KEYWORD nonn,easy AUTHOR Ralf Stephan, Jul 06 2003 STATUS approved

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Last modified February 24 00:51 EST 2020. Contains 332195 sequences. (Running on oeis4.)