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 A181936 Number of 5-alternating permutations. 5
 1, 1, 1, 1, 1, 1, 5, 20, 55, 125, 251, 2300, 15775, 70500, 249250, 750751, 10006375, 97226875, 601638125, 2886735625, 11593285251, 202808749375, 2550175096250, 20163891580625, 122209131374375, 613498040952501, 13287626090593750, 205055676105734375 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,7 COMMENTS For an integer n>0, a permutation s = s_1...s_k is a n-alternating permutation if it has the property that s_i < s_{i+1} if and only if n divides i. REFERENCES Anthony Mendes and Jeffrey Remmel, Generating functions from symmetric functions, Preliminary version of book, available from Jeffrey Remmel's home page. LINKS Alois P. Heinz, Table of n, a(n) for n = 0..200 R. J. Cano, PARI Sequencer program. Peter Luschny, An old operation on sequences: the Seidel transform. Ludwig Seidel, Über eine einfache Entstehungsweise der Bernoulli'schen Zahlen und einiger verwandten Reihen, Sitzungsberichte der mathematisch-physikalischen Classe der königlich bayerischen Akademie der Wissenschaften zu München, volume 7 (1877), 157-187. [USA access only through the HATHI TRUST Digital Library] Ludwig Seidel, Über eine einfache Entstehungsweise der Bernoulli'schen Zahlen und einiger verwandten Reihen, Sitzungsberichte der mathematisch-physikalischen Classe der königlich bayerischen Akademie der Wissenschaften zu München, volume 7 (1877), 157-187. [Access through ZOBODAT] MAPLE A181936_list := proc(dim) local E, DIM, n, k; DIM := dim-1; E := array(0..DIM, 0..DIM); E[0, 0] := 1; for n from 1 to DIM do if n mod 5 = 0 then E[n, 0] := 0 ;    for k from n-1 by -1 to 0 do E[k, n-k] := E[k+1, n-k-1] + E[k, n-k-1] od; else E[0, n] := 0;    for k from 1 by 1 to n do E[k, n-k] := E[k-1, n-k+1] + E[k-1, n-k] od; fi od; [E[0, 0], seq(E[k, 0]+E[0, k], k=1..DIM)] end: A181936_list(28); # Alternatively, using an exponential generating function: A181936_list := proc(n) local H, F, i; H := (r, s) -> hypergeom(r, s/5, -(t/5)^5); F := t -> 1+(t^5*H([1], [6, 7, 8, 9, 10])+5*t^4*H([], [6, 7, 8, 9])+20*t^3*H([], [4, 6, 7, 8])+60*t^2*H([], [3, 4, 6, 7])+120*t^1*H([], [2, 3, 4, 6]))/(120*H([], [2, 3, 4, 1])); seq(i!*coeff(series(F(t), t, n+1), t, i), i=0..n-1) end: MATHEMATICA dim = 27; e[0, 0] = 1; e[n_ /; Mod[n, 5] == 0 && 0 <= n <= dim, 0] = 0; e[k_ /; 0 <= k <= dim, n_ /; 0 <= n <= dim] /; Mod[n+k, 5] == 0 := e[k, n] = e[k, n-1] + e[k+1, n-1]; e[0, n_ /; Mod[n, 5] == 0 && 0 <= n <= dim] = 0; e[k_ /; 0 <= k <= dim, n_ /; 0 <= n <= dim] /; Mod[n+k, 5] != 0 := e[k, n] = e[k-1, n] + e[k-1, n+1]; e[_, _] = 0; a[0] = 1; a[n_] := e[n, 0] + e[0, n]; Table[a[n], {n, 0, dim}] (* Jean-François Alcover, Jun 27 2013, translated and adapted from Maple *) b[u_, o_, t_] := b[u, o, t] = If[u + o == 0, 1, If[t == 0,      Sum[b[u - j, o + j - 1, Mod[t + 1, 5]], {j, 1, u}],      Sum[b[u + j - 1, o - j, Mod[t + 1, 5]], {j, 1, o}]]]; a[n_] := b[n, 0, 0]; a /@ Range[0, 35] (* Jean-François Alcover, Apr 21 2021, after _Alois P. Heinz in A250283 *) nmax = 30; CoefficientList[Series[1 + Sum[(x^(5 - k) * HypergeometricPFQ[{1}, {6/5 - k/5, 7/5 - k/5, 8/5 - k/5, 9/5 - k/5, 2 - k/5}, -x^5/3125])/(5 - k)!, {k, 0, 4}] / HypergeometricPFQ[{}, {1/5, 2/5, 3/5, 4/5}, -x^5/3125], {x, 0, nmax}], x] * Range[0, nmax]! (* Vaclav Kotesovec, Apr 21 2021 *) PROG (Sage) @cached_function def A(m, n):     if n == 0: return 1     s = -1 if m.divides(n) else 1     t = [m*k for k in (0..(n-1)//m)]     return s*add(binomial(n, k)*A(m, k) for k in t) A181936 = lambda n: (-1)^int(is_odd(n//5))*A(5, n) print([A181936(n) for n in (0..30)]) # Peter Luschny, Jan 24 2017 CROSSREFS Number of m-alternating permutations: A000012 (m=1), A000111 (m=2), A178963 (m=3), A178964 (m=4), this sequence (m=5), A250283 (m=6), A250284 (m=7), A250285 (m=8), A250286 (m=9), A250287 (m=10). Row n=5 of A181937. Sequence in context: A289306 A325731 A062988 * A226639 A264874 A270092 Adjacent sequences:  A181933 A181934 A181935 * A181937 A181938 A181939 KEYWORD nonn AUTHOR Peter Luschny, Apr 03 2012 STATUS approved

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Last modified May 9 17:41 EDT 2021. Contains 343742 sequences. (Running on oeis4.)