51206domain: NAppears in sequencesNumber of 3-covers of an unlabeled n-set.at n=21A005783Numbers k such that 163*2^k+1 is prime.at n=41A032458G.f. A(x) satisfies A(x) = 1+x^2/(1-x)*A(x^2/(1-x)).at n=23A201196a(n) = n*(n + 5)*(n + 7)*(n + 10)/24 + 1.at n=28A323220