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Re^2: is it prime?

by JavaFan (Canon)
on May 06, 2012 at 15:12 UTC ( #969149=note: print w/replies, xml ) Need Help??


in reply to Re: is it prime?
in thread is it prime?

One speedy way is to use the Sieve of Eratosthenes.
It's speedy if you want all primes below a certain number, or if you need to determine primality of "a lot of" numbers, but it isn't for checking a single number.

Checking all the possible divisors can be done in O(√N) (throw in a factor of O(log n) to do the division if you have really big numbers). However, just initializing the sieve will take you Ω(N) time. And then you still have to do the work: Ω(N/pi) for the ith prime.

The fastest way is probably just to use bigprimes.net, which has the first 1.4 billion primes on file.

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[shmem]: choroba: it's hessisch
[Corion]: Not every Krug is a Bembel!
[karlgoethebier]: there is just the mug: 🍺
[Corion]: A Bembel must look like this
[karlgoethebier]: https://de. wikipedia.org/ wiki/Bembel#/ media/File: Bembel_Zum_blauen_ Bock_1978.jpg
[choroba]: as my friend says, Ich stehe Deutsche ver nicht aber klein ;-)
[Corion]: Krug is generic pottery ware for pouring beverages, but a Bembel is painted with that blue paint and contains only (!) Apfelwein
[shmem]: Corion: alas, air too.
[Corion]: shmem: Yes, very sad!
[choroba]: doesn't sound much useful, which means I'll probably remember it

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