unprimeable

adjective2

1. •
   That cannot be primed.

   • In this count, the Syntactic sentences actually had more "unprimeable" words than the Random, 86 versus 74. — 1989
2. •
   That cannot be turned into a prime number by changing just one of its digits to any other digit.

   • 6,292,015 is a composite, Duffinian, odd, semiprime, square-free and unprimeable number. — 2015