B = zeros(m,n,p,...) or B = zeros([m n p ...]) returns an m-by-n-by-p-by-... array of zeros.
Now, 1:n is the same as the vector [1 2 3 4 5 6 ... n]
so
zeros(1:n)
is the same as
zeros([1,2,3,4,...n])
which would request factorial(n) array locations. If your n is 21, that would be 51090942171709440000 array locations, which is between 2^65 and 2^66 array locations, and thus would require between 2^68 and 2^69 bytes of storage.
