9733

This number is a prime.

9733 is the largest 4-digit prime having both of these properties: (1) it is the sum of 7 distinct powers of 3: 9733 = 3^0 + 3^1 + 3^2 + 3^5 + 3^6 + 3^7 + 3^8, and (2) if its base-3 representation (111100111) is read as if it were base 2, the resulting number (487) is also prime. [Keith]