Hi i'm trying to figure out how to write a procedure for creating a NxN matrix with conditions. The conditions for M[ij] are as follows:

a if j>i+1, c if i>j+1 and b otherwise.

So far this is what i've come up with but i've tied myself into a mental loop and cant seem to figure this out. I know it's really simple and that's what is frustrating me the most.

How does one create the set of all positive integers less than and coprime to 66?

I created a set of integers from 1-66: L := {seq(i, i = 1 .. 66)}, then try define coprime66 as follws, coprime66 := isprime(igcd(L, 66)),  to get a set of the coprimes but i get an error.

I've tried op(L) but this doesn't work either. What am i doing wrong?