the square of 9 and the fourth power of 3. a perfect totient number like all powers of three.[1] a heptagonal number.[2] a centered octagonal number.[3] a tribonacci number.[4] an open meandric number. the ninth member of the Mian-Chowla sequence.[5] a palindromic number in bases 8 (1218) and 26 (3326). a Harshad number in bases 2, 3, 4, 7, 9, 10 and 13 The Number is 81