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发表于 2008-11-23 09:50:35
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Lucas pseudoprime(Lucas素性测试)
From Wikipedia, the free encyclopedia
In number theory, the classes of Lucas pseudoprime and Fibonacci pseudoprime comprise sequences of composite integers that passes certain tests that all primes pass: in this case, criteria relative to some Lucas sequence.
DefinitionGiven two integer parameters P and Q which satisfy
[img=http://upload.wikimedia.org/math/d/3/e/d3e982438078471ba39770d7260420a9.png]D = P^2 - 4Q \neq 0 ,[/img]
the Lucas sequences of the first and second kind, Un(P,Q) and Vn(P,Q) respectively, are defined by the recurrence relations
[img=http://upload.wikimedia.org/math/8/b/0/8b08175c9e31647813a13ddc98b374c4.png]U_0(P,Q)=0 \,[/img]
[img=http://upload.wikimedia.org/math/9/8/b/98ba9238398ec3c91d8441e5826194d1.png]U_1(P,Q)=1 \,[/img]
[img=http://upload.wikimedia.org/math/9/a/4/9a46a8ecbb888eb6501179bdb5f6b765.png]U_n(P,Q)=PU_{n-1}(P,Q)-QU_{n-2}(P,Q) \mbox{ for }n>1 \,[/img]
and
[img=http://upload.wikimedia.org/math/d/a/6/da6477c58672e5f5623ac18b803ed499.png]V_0(P,Q)=2 \,[/img]
[img=http://upload.wikimedia.org/math/5/3/3/53345185887ea556882e1f24c287b30f.png]V_1(P,Q)=P \,[/img]
[img=http://upload.wikimedia.org/math/4/5/2/452270dd8e50a060a8875956ad0d68a5.png]V_n(P,Q)=PV_{n-1}(P,Q)-QV_{n-2}(P,Q) \mbox{ for }n>1 \,[/img]
We can write
[img=http://upload.wikimedia.org/math/1/e/3/1e345f4b1a7a69a8aa4b88aefd7978d9.png]U_n(P,Q) = \frac{a^n-b^n}{a-b} \,[/img]
[img=http://upload.wikimedia.org/math/3/9/9/3998f696038a67c212febef42406c121.png]V_n(P,Q) = a^n + b^n \,[/img]
where a and b are roots of the auxiliary polynomial $X^2 - PX + Q$, of discriminant D.
If p is an odd prime number then
Vp is congruent to P modulo p.and if the Jacobi symbol
[img=http://upload.wikimedia.org/math/7/2/6/726ae3b242cf982e658bc00769726abb.png]\left(\frac{D}{p}\right) = \varepsilon \ne 0[/img],
then p is a factor of Up-ε.
[edit] Lucas pseudoprimesA Lucas pseudoprime is a composite number n for which n is a factor of Un-ε. (Riesel adds the condition that D should be −1.)
In the specific case of the Fibonacci sequence, where P = 1, Q = 1 and D = 5, the first Lucas pseudoprimes are 323 and 377; [img=http://upload.wikimedia.org/math/8/4/2/842c77a349e7bd8b1e4c9b7e12085eb8.png]\left(\frac{5}{323}\right)[/img] and [img=http://upload.wikimedia.org/math/a/6/3/a633dee94d7f67af1aceab21ad654abb.png]\left(\frac{5}{377}\right)[/img] are both −1, the 324th Fibonacci number is a multiple of 323, and the 378th is a multiple of 377.
A strong Lucas pseudoprime is an odd composite number n with (n,D)=1, and n-ε=2rs with s odd, satisfying one of the conditions
n divides Usn divides V2jsfor some j ≤ r. A strong Lucas pseudoprime is also a Lucas pseudoprime.
An extra strong Lucas pseudoprime is a strong Lucas pseudoprime for a set of parameters (P,Q) where Q = 1.
[edit] Fibonacci pseudoprimesA Fibonacci pseudoprime is a composite number n for which
Vn is congruent to P modulo nwhen Q = ±1.
A strong Fibonacci pseudoprime may be defined as a composite number which is a Fibonacci pseudoprime for all P. It follows (see Müller and Oswald) that in this case:
- An odd composite integer n is also a Carmichael number
- 2(pi + 1) | (n − 1) or 2(pi + 1) | (n − pi) for every prime pi dividing n.
The smallest example of a strong Fibonacci pseudoprime is443372888629441, which has factors 17, 31, 41, 43, 89, 97, 167 and 331.
It is conjectured that there are no even Fibonacci pseudoprimes (see Somer). |
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