a(n) = (26^n - 1)/25.A218729a(n) = (26^n - 1)/25.Terms a(0) =0a(1) =1a(2) =27a(3) =703a(4) =18279a(5) =475255a(6) =12356631a(7) =321272407a(8) =8353082583a(9) =217180147159External referencesoeis: A218729