How can I conclude from the following table whether N=15841 is a pseudoprime and/or strong pseudoprime for the bases a=2, a=145, and a=789?
Given is that 15840 = 2^5 * 495
So far I know that a composite number N is called a pseudoprime for the base a if
a^(N-1) = 1 (mod N)
and a strong pseudoprime if
a^((N-1)/2) = (a/N) (mod N)
However that would result in a huge number such as a^15840 which is impossible to calculate. I suppose I should use the fact that 15840 = 2^5 * 495 but I'm not sure how?
EDIT: I'm guessing N would be pseudoprime for a base if there's at least one 1, but I'm not entirely sure when it's a strong pseudoprime.