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 A000274 Number of permutations of length n with 2 consecutive ascending pairs. (Formerly M3048 N1236) 10
 0, 0, 1, 3, 18, 110, 795, 6489, 59332, 600732, 6674805, 80765135, 1057289046, 14890154058, 224497707343, 3607998868005, 61576514013960, 1112225784377144, 21197714949305577, 425131949816628507, 8950146311929021210 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS From Emeric Deutsch, May 25 2009: (Start) a(n) = number of excedances in all derangements of [n-1]. Example: a(5)=18 because the derangements of {1,2,3,4} are 4*123, 3*14*2, 3*4*12, 4*3*12, 2*14*3, 2*4*13, 2*3*4*1, 3*4*21, 4*3*21 with the 18 excedances marked. An excedance of a permutation p is a position i such that p(i)>i. a(n) = Sum(k*A046739(n,k), k>=1). (End) Appears to be the inverse binomial transform of A001286 (filling the two leading zeros in there), then shifting one place to the right. R. J. Mathar, Apr 04 2012 REFERENCES F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 263. J. Riordan, An Introduction to Combinatorial Analysis, Wiley, 1958, p. 210 (divided by 2). N. J. A. Sloane, A Handbook of Integer Sequences, Academic Press, 1973 (includes this sequence). N. J. A. Sloane and Simon Plouffe, The Encyclopedia of Integer Sequences, Academic Press, 1995 (includes this sequence). LINKS Alois P. Heinz, Table of n, a(n) for n = 1..150 R. Mantaci and F. Rakotondrajao, Exceedingly deranging!, Advances in Appl. Math., 30 (2003), 177-188. [Emeric Deutsch, May 25 2009] FORMULA a(n) = (1 + n) a(n - 1) + (3 + n) a(n - 2) + (3 - n) a(n - 3) + (2 - n) a(n - 4). E.g.f.: x^2/2*exp(-x)/(1-x)^2. - Vladeta Jovovic, Jan 03 2003 a(n) = (n-1)^2/(n-2)*a(n-1)-(-1)^n*(n-1)/2, n>2, a(2)=0. - Vladeta Jovovic, Aug 31 2003 a(n) = (1/2){[n!/e] - [(n-1)!/e]} (conjectured). a(n) = (n-1)*GAMMA(n,-1)*exp(-1)/2 where GAMMA = incomplete Gamma function. [Mark van Hoeij, Nov 11 2009] a(n) = A145887(n-1) + A145886(n-1). - Anton Zakharov, Aug 28 2016 MAPLE a:= n->sum(n!*sum((-1)^k/k!/2, j=1..n), k=0..n): seq(a(n), n=2..20); # Zerinvary Lajos, May 17 2007 MATHEMATICA Table[Subfactorial[n]*n/2, {n, 2, 20}] (* Zerinvary Lajos, Jul 09 2009 *) CROSSREFS Cf. A010027, A000255, A000166, A000313, A001260, A001261. A diagonal in triangle A010027. Cf. A046739. [Emeric Deutsch, May 25 2009] Cf. A145887, A145886. Sequence in context: A074571 A114311 A134092 * A207321 A193236 A357203 Adjacent sequences: A000271 A000272 A000273 * A000275 A000276 A000277 KEYWORD easy,nonn AUTHOR N. J. A. Sloane, Simon Plouffe EXTENSIONS Name clarified and offset changed by N. J. A. Sloane, Apr 12 2014 STATUS approved

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Last modified June 1 17:30 EDT 2023. Contains 363076 sequences. (Running on oeis4.)