A safe prime is a prime number of the form 2p + 1, where p is also a prime. (Conversely, the prime p is a Sophie Germain prime.) The first few safe primes are
- 5, 7, 11, 23, 47, 59, 83, 107, 167, 179, 227, 263, 347, 359, 383, 467, 479, 503, 563, 587, 719, 839, 863, 887, 983, 1019, 1187, 1283, 1307, 1319, 1367, 1439, 1487, 1523, 1619, 1823, 1907, ... (sequence A005385 in OEIS)
With the exception of 7, a safe prime q is of the form 6k − 1 or, equivalently, q ≡ 5 (mod 6) — as is p > 3 (c.f. Sophie Germain prime, second paragraph). Similarly, with the exception of 5, a safe prime q is of the form 4k − 1 or, equivalently, q ≡ 3 (mod 4) — trivially true since (q − 1) / 2 must evaluate to an odd natural number. Combining both forms using lcm(6,4) we determine that a safe prime q > 7 also must be of the form 12k−1 or, equivalently, q ≡ 11 (mod 12).
Read more about Safe Prime: Applications, Further Properties, Records
Famous quotes containing the words safe and/or prime:
“What the hell is nostalgia doing in a science-fiction film? With the whole universe and all the future to play in, Lucas took his marvelous toys and crawled under the fringed cloth on the parlor table, back into a nice safe hideyhole, along with Flash Gordon and the Cowardly Lion and Luck Skywalker and the Flying Aces and the Hitler Jugend. If there’s a message there, I don’t think I want to hear it.”
—Ursula K. Le Guin (b. 1929)
“By whatever means it is accomplished, the prime business of a play is to arouse the passions of its audience so that by the route of passion may be opened up new relationships between a man and men, and between men and Man. Drama is akin to the other inventions of man in that it ought to help us to know more, and not merely to spend our feelings.”
—Arthur Miller (b. 1915)