961

This number is a composite.

31^2 = 961 is the largest prime power of a prime with strictly decreasing digits. [Chandler]

The smallest square that is the sum of the first n odd primes (3+5+7+...+83+89=961). [Bajpai]

In the Fermat's diophantine quadruple {1, 3, 8, 120}, one more than the product of any two terms is a prime square. The prime squares produced are {4, 9, 25, 121, 361, 961}. [Gudipati]