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 A231601 Number of permutations of [n] avoiding ascents from odd to even numbers. 3
 1, 1, 1, 4, 8, 54, 162, 1536, 6144, 75000, 375000, 5598720, 33592320, 592950960, 4150656720, 84557168640, 676457349120, 15620794116480, 140587147048320, 3628800000000000, 36288000000000000, 1035338990313196800, 11388728893445164800, 355902198372945100800 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,4 LINKS Alois P. Heinz, Table of n, a(n) for n = 0..250 FORMULA a(n) = ceiling(n/2)! * ceiling(n/2)^floor(n/2). a(n) = A081123(n+1) * A110138(n). EXAMPLE a(0) = 1: (). a(1) = 1: 1. a(2) = 1: 21. a(3) = 4: 132, 213, 231, 321. a(4) = 8: 1324, 2413, 2431, 3241, 4132, 4213, 4231, 4321. a(5) = 54: 13245, 13254, 13524, ..., 54213, 54231, 54321. a(6) = 162: 132465, 132546, 132645, ..., 654213, 654231, 654321. MAPLE a:= n-> ceil(n/2)!*ceil(n/2)^floor(n/2): seq(a(n), n=0..30); CROSSREFS Column k=0 of A231777. Bisection gives: A061711 (even part). Cf. A081123, A110138, A199660, A285672. Sequence in context: A128893 A214603 A192508 * A123106 A123288 A192200 Adjacent sequences:  A231598 A231599 A231600 * A231602 A231603 A231604 KEYWORD nonn AUTHOR Alois P. Heinz, Nov 11 2013 STATUS approved

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Last modified January 29 08:12 EST 2020. Contains 331337 sequences. (Running on oeis4.)