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Lucas Pseudoprime


A Lucas pseudoprime with parameters P and Q is an odd composite integer n satisfying gcd(n,2QD)=1 and U_(n-(D/n))=0 (mod n), where P is a positive integer, Q is an integer, D=P^2-4Q!=0, (D/n) is the Jacobi symbol, and gcd denotes the greatest common divisor. The Lucas sequence {U_k} is given by

 U_k=(a^k-b^k)/(a-b),

where k>=0 and a and b are the two polynomial roots of x^2-Px+Q=0. In the commonly used case (D/n)=-1, the defining congruence becomes U_(n+1)=0 (mod n) (Baillie and Wagstaff 1980, Baillie et al. 2021).

Bruckman (1994) uses a different convention. The congruence L_n=1 (mod n) holds for every prime number n, where L_n is a Lucas number. The composite numbers that also satisfy it are called Bruckman-Lucas pseudoprimes. The first few are 705, 2465, 2737, 3745, 4181, 5777, 6721, ... (OEIS A005845). This is a test using the Lucas numbers, rather than the preceding test using the Lucas sequence U_k.

The Wolfram Language implements the Miller-Rabin strong pseudoprime tests in bases 2 and 3 combined with a Lucas pseudoprime test as the primality test in the function PrimeQ[n].


See also

Extra Strong Lucas Pseudoprime, Lucas Number, Lucas Sequence, Pseudoprime, Strong Lucas Pseudoprime

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References

Baillie, R.; Fiori, A.; and Wagstaff, S. S. Jr. "Strengthening the Baillie-PSW Primality Test." Math. Comput. 90, 1931-1955, 2021. https://doi.org/10.1090/mcom/3616.Baillie, R. and Wagstaff, S. S. Jr. "Lucas Pseudoprimes." Math. Comput. 35, 1391-1417, 1980.Bruckman, P. S. "Lucas Pseudoprimes are Odd." Fib. Quart. 32, 155-157, 1994.Ribenboim, P. "Lucas Pseudoprimes (lpsp(P,Q))." §2.X.B in The New Book of Prime Number Records, 3rd ed. New York: Springer-Verlag, p. 129, 1996.Sloane, N. J. A. Sequence A005845/M5469 in "The On-Line Encyclopedia of Integer Sequences."

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Lucas Pseudoprime

Cite this as:

Weisstein, Eric W. "Lucas Pseudoprime." From MathWorld--A Wolfram Resource. https://mathworld.wolfram.com/LucasPseudoprime.html

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