a(n) = (27^n-4^n)/23.A180847a(n) = (27^n-4^n)/23.Terms a(0) =0a(1) =1a(2) =31a(3) =853a(4) =23095a(5) =623821a(6) =16844191a(7) =454797253a(8) =12279542215a(9) =331547705341External referencesoeis: A180847