A264468 - OEIS

%I #5 Nov 14 2015 16:59:29

%S 18,780,15627,235045,3086010,37816568,449766437,5291113080,

%T 62237008779,736806459069,8816027319934,106900514193980,

%U 1315953951437664,16464756848575162,209528329365176670,2713295547732215190,35762229764646245816,479809424452611001696

%N Number of permutations of [n] with exactly nine (possibly overlapping) occurrences of the generalized pattern 23-1.

%H Alois P. Heinz, <a href="/A264468/b264468.txt">Table of n, a(n) for n = 7..500</a>

%e a(7) = 18: 3567241, 4567123, 4567132, 4567213, 4567312, 4567321, 4672351, 4673512, 4673521, 5671342, 5672314, 5672413, 5672431, 5673241, 5674231, 6734512, 6734521, 6745231.

%p b:= proc(u, o) option remember; `if`(u+o=0, 1, add(

%p       b(u-j, o+j-1), j=1..u) +add(convert(series(

%p       b(u+j-1, o-j)*x^u, x, 10), polynom), j=1..o))

%p     end:

%p a:= n-> coeff(b(n, 0), x, 9):

%p seq(a(n), n=7..25);

%Y Column k=9 of A260670.

%K nonn

%O 7,1

%A _Alois P. Heinz_, Nov 14 2015