20920706405domain: NAppears in sequencesa(0)=1, a(n) = 3*a(n-1) + 2; a(n) = 2*3^n - 1.at n=21A048473A048473 prefixed by two zeros.at n=23A1549922*3^(n-1)-(-1)^n.at n=21A174132a(n) = 6*9^n-1.at n=10A198963