The name of any integer can be transformed into a number by setting A=1, B=2, C=3, etc.: ONE = 15145, TWO = 202315, THREE = 2081855, and so on.

Because every English number name ends in D (4), E (5), L (12), N (14), O (15), R (18), T (20), X (24), or Y (25), no such transformation will produce a prime number.

But in Spanish, which uses 27 letters, both SESENTA (60) = 20520514211 and MIL SETENTA (1070) = 1391220521514211 yield primes.

(Thanks, Claudio.)