It is confusing for students regarding the two forms of the Fermat’s Little Theorem, which is the generalization of the ancient Chinese Remainder Theorem (中国剩馀定理) — the only theorem used in modern Computer Cryptography .
General: For any number a
If (a, p) co-prime, or g.c.d.(a, p)=1,
then p cannot divide a,
Special: g.c.d. (a, p)=1