This number is a composite.
Ever since the Willow Grove Exit of the Pennsylvania Turnpike has existed, its exit number has been 27, the cube of an odd prime (33 = 27). Now, the turnpike exit numbers are being changed, and the exit number for Willow Grove will soon be 343 - another cube of an odd prime (73 = 343). [Litman]
7 cubed can be expressed using the first six odd primes: 7(3+5+11+13+17). [Silva]