On Mon, 14 Apr 2014 23:41:03 -0400, tlvp wrote:

Is the whole deal the difference between suffix "_n" and suffix "_b"

I don't know, but, testing a through z, I find:
b = http://farm8.staticflickr.com/7437/1...b9c07b48_b.jpg
c = http://farm8.staticflickr.com/7437/1...b9c07b48_c.jpg
d = http://farm8.staticflickr.com/7437/1...b9c07b48_d.jpg
e = http://farm8.staticflickr.com/7437/1...b9c07b48_m.jpg
n = http://farm8.staticflickr.com/7437/1...b9c07b48_n.jpg
q = http://farm8.staticflickr.com/7437/1...b9c07b48_q.jpg
s = http://farm8.staticflickr.com/7437/1...b9c07b48_s.jpg
t = http://farm8.staticflickr.com/7437/1...b9c07b48_t.jpg
z = http://farm8.staticflickr.com/7437/1...b9c07b48_z.jpg

Who knows what the purpose or intent of these variations are.
As an aside, notice how "_d", "_q", & "_s" were quite odd results,
but "_b" was the best.