2097140domain: NAppears in sequencesa(n) = (-1/2)*Sum_{i1 + i2 + i3 = 2*n} ((2*n)!/(i1! i2! i3!))*B(i1), where B are the Bernoulli numbers (with i1, i2, i3 >= 1).at n=10A124133Expansion of g.f. 8/(1-2*z)-12/(1-z)+z+5.at n=18A173034a(n) = 2^n - floor((n+3)/2).at n=21A320933