24

This number is a composite.

Exactly half, 24 of the contiguous 48 states of the United States plus the District of Columbia (DC) are adjacent to a prime number of other states or districts. DC, FL, RI, SC, WA are connected to 2 other states; CA, CT, DE, LA, MI, ND, NH, NJ, VT are connected to 3 other states; GA, IL, MA, MD, NV, NY, OH, UT, WV are connected to 5 other states; KY is connected to 7 other states. [Post]