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A047921 Triangle of numbers a(n,k) = number of permutations on n letters containing k 3-sequences (n >= 2, 0<=k<=n-2). 3
2, 5, 1, 21, 2, 1, 106, 11, 2, 1, 643, 62, 12, 2, 1, 4547, 406, 71, 13, 2, 1, 36696, 3046, 481, 80, 14, 2, 1, 332769, 25737, 3708, 559, 89, 15, 2, 1, 3349507, 242094, 32028, 4414, 640, 98, 16, 2, 1, 37054436, 2510733, 306723, 38893, 5164, 724, 107, 17, 2, 1 (list; table; graph; refs; listen; history; text; internal format)
OFFSET

2,1

LINKS

Table of n, a(n) for n=2..56.

J. Riordan, Permutations without 3-sequences, Bull. Amer. Math. Soc., 51 (1945), 745-748.

FORMULA

Riordan gives a recurrence.

EXAMPLE

2; 5 1; 21 2 1; 106 11 2 1; ...

CROSSREFS

Columns give A002628, A002629, A002630.

Sequence in context: A187244 A120294 A186766 * A242783 A177250 A102786

Adjacent sequences:  A047918 A047919 A047920 * A047922 A047923 A047924

KEYWORD

nonn,tabl,nice,easy

AUTHOR

N. J. A. Sloane

EXTENSIONS

Edited and extended by Max Alekseyev, Sep 05 2010

STATUS

approved

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Last modified March 20 05:29 EDT 2019. Contains 321344 sequences. (Running on oeis4.)