Algorithm writing tips?

Something I thought about later... sqrt is not cheap (iirc it uses Newton's method to approximate?).

primesList.get(i) <= Math.sqrt(n)
Use
primeslist.get(i)**2 <= n

Depends on what language you use. Shouldn't it equal to Math.pow(n, 0.5), which uses logaritms?

edit: Implementation-dependent:


Anyway, I save the value instead of recalculating it. e.g:

sqrt = (int) Math.sqrt(n)
for (i = 5; i < sqrt; i += 6)

instead of:

for (i = 5; i < Math.sqrt(n); i += 6)