45290

Appears in sequences

• Triangle read by rows: T(n,k) is the number of permutations p of [n] in which exactly the first k terms satisfy the up-down property, i.e., p(1)<p(2), p(2)>p(3), p(3)<p(4), ...at n=52A092580
• E.g.f. 1-x*(1-x)*(tan(x)+sec(x)).at n=10A211182
• Number of 2Xn 0..2 arrays with exactly floor(2Xn/2) elements unequal to at least one horizontal or antidiagonal neighbor, with new values introduced in row major 0..2 order.at n=9A222691