1258292domain: NAppears in sequencesExpansion of (1-x^2)/((1-2*x)*(1+x^2)).at n=21A100088Inverse binomial transform of A007910.at n=43A137505a(n) = a(n-1) + a(n-2) + a(n-3) + 2*a(n-4) with a(0)=2, a(1)=1, a(2)=5, a(3)=10.at n=20A226309