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Submitted via IRC for Bytram
What Is an "Almost Prime" Number?
When I saw a math paper with the phrase "almost prime" in the title, I thought it sounded pretty funny. It reminded me of the joke about how you can't be a little bit pregnant. On further thought, though, it seems like someone whose pregnancy is 6 weeks along and who hasn't yet noticed a missed period is meaningfully less pregnant that someone rounding the bend at 39 weeks who can balance a dinner plate on their belly. Perhaps "almost prime" could make sense too.
A number is prime if its only factors are 1 and itself. By convention, the number 1 is not considered to be prime, so the primes start 2, 3, 5, 7, 11, and so on. Hence, a prime number has one prime factor. A number with two prime factors, like 4 (where the two factors are both 2) or 6 (2×3) is definitely less prime than a prime number, but it kind of seems more prime than 8 or 30, both of which have three prime factors (2×2×2 and 2×3×5, respectively). The notion of almost primes is a way of quantifying how close a number is to being prime.
(Score: 2) by ikanreed on Monday November 05 2018, @04:44PM (1 child)
When you see kind of basic things from a field of study as a news story.
Prime factoring fits into a lot of abstract algebra, and "near primes" are(obviously) more likely to be coprime to other numbers than prime primes. Coprimality is, as others have noted, an important aspect of encryption, as, after the first 2k prime test, checking corprimality between public and private keys is the next step of validating their "real" primeness.
(Score: 2) by Freeman on Monday November 05 2018, @06:07PM
This is why I'm not a mathematician. I get the need for encryption, but actually understanding the math behind it is a whole other ballgame.
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