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A000363
Number of permutations of [n] with exactly 2 increasing runs of length at least 2.
(Formerly M4018 N1666)
4
5, 61, 479, 3111, 18270, 101166, 540242, 2819266, 14494859, 73802835, 373398489, 1881341265, 9453340172, 47417364268, 237571096820, 1189405165908, 5951965440609, 29775517732665, 148927275340835, 744793282001995
OFFSET
4,1
REFERENCES
F. N. David, M. G. Kendall and D. E. Barton, Symmetric Function and Allied Tables, Cambridge, 1966, p. 260.
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
FORMULA
a(n) = (5^n-(2*n-1)*3^n+2*n^2-2*n-2)/16. - Vaclav Kotesovec, Nov 19 2012
G.f.: -x^4*(9*x-5)/((x-1)^3*(3*x-1)^2*(5*x-1)). - Vaclav Kotesovec, Nov 19 2012
MATHEMATICA
Table[(5^n-(2*n-1)*3^n+2*n^2-2*n-2)/16, {n, 4, 20}] (* Vaclav Kotesovec, Nov 19 2012 *)
PROG
(Magma) [(5^n-(2*n-1)*3^n+2*n^2-2*n-2)/16: n in [4..30]]; // Vincenzo Librandi, May 03 2013
CROSSREFS
Contribution from Johannes W. Meijer, May 24 2009: (Start)
The a(n) sequence equals the third left hand column of A008971.
The a(2*n) sequence equals the third left hand column of A160486.
(End)
Sequence in context: A060060 A183379 A345649 * A200956 A203358 A099666
KEYWORD
nonn,easy
EXTENSIONS
More terms and better definition from Jon E. Schoenfield, Mar 25 2010
STATUS
approved