A317284 - OEIS

A317284

Number of permutations of [n] with exactly four increasing runs of even length.

1385, 31493, 460929, 6632158, 99592344, 1489928080, 22566676855, 354404597721, 5758011600442, 96477356811365, 1673128285327455, 30065282456829860, 558998263719383722, 10749166166477149832, 213755085162112473899, 4392507334767609209209, 93197430506980061714657

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OFFSET

8,1

LINKS

Alois P. Heinz, Table of n, a(n) for n = 8..471

MAPLE

b:= proc(u, o, t) option remember; series(`if`(u+o=0, x^t,

add(b(u+j-1, o-j, irem(t+1, 2)), j=1..o)+

add(b(u-j, o+j-1, 0)*x^t, j=1..u)), x, 5)

end:

a:= n-> coeff(b(n, 0$2), x, 4):

seq(a(n), n=8..30);