a(n) = 3^n*(3^n-1)*(3^n-2)/6.A026809a(n) = 3^n*(3^n-1)*(3^n-2)/6.Terms a(0) =0a(1) =1a(2) =84a(3) =2925a(4) =85320a(5) =2362041a(6) =64304604a(7) =1741001445a(8) =47050068240External referencesoeis: A026809