Assuming you have a typo in your example and your desired output is actually
[2, 3, 5, 8, 9]
(i.e. an 8 instead of the repeated 6), then I think this should do what you want:
n = 3;
N = 3;
a = [2, 3];
b = n*[0:N-1];
c = bsxfun(@plus, a.', b);
c = c(:).'
or as a messy one-liner:
reshape(bsxfun(@plus, [2, 3].', 3*(0:3-1)), 1, );
No gurantees that someone won't have a more clever solution, but if this doesn't give the desired result, perhaps a little more clarification would be helpful.