1609

This number is a prime.

(1609, 1613) is the first case of a 4-digit cousin prime pair (p, q) such that p^2+q^3 -/+ 1 is a twin prime pair, i.e., 1609^2+1613^3-1= 4199242277 and 1609^2+1613^3+1= 4199242279 are both prime. [Loungrides]