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Lucas Pseudoprime


When P and Q are integers such that D=P^2-4Q!=0, define the Lucas sequence {U_k} by

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

for k>=0, with a and b the two roots of x^2-Px+Q=0. Then define a Lucas pseudoprime as an odd composite number n such that nQ, the Jacobi symbol (D/n)=-1, and n|U_(n+1).

The congruence L_n=1 (mod n) holds for every prime number n, where L_n is a Lucas number. However, some composites also satisfy this congruence. The Lucas pseudoprimes corresponding to the special case of the Lucas numbers L_n are those composite numbers n such that n|(L_n-1). The first few of these are 705, 2465, 2737, 3745, 4181, 5777, 6721, ... (OEIS A005845).

The Wolfram Language implements the multiple Rabin-Miller test 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. 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 Web Resource. https://mathworld.wolfram.com/LucasPseudoprime.html

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