I didn't check for specific factors here since `ecm` and trial division return
different factors. For example when tested with 121 `ecm` returns 121 as a
factor and trial division finds the smallest prime as always. So I only checked
the return values which are greater than 1 if a factor is found by respective
algorithms. Also I tried setting `B1 = 1`  and `B1 = 9007199254740991`
(maximum allowed for B1) still `ecm` couldn't find a smaller factor. I think we
it will be better to implement an algorithm which is good for relatively smaller
numbers. I am interested in Pollard rho method which is used in `SymPy` as
well.