

A212424


Frobenius pseudoprimes with respect to Fibonacci polynomial x^2  x  1.


8



4181, 5777, 6721, 10877, 13201, 15251, 34561, 51841, 64079, 64681, 67861, 68251, 75077, 90061, 96049, 97921, 100127, 113573, 118441, 146611, 161027, 162133, 163081, 186961, 197209, 219781, 231703, 252601, 254321, 257761, 268801, 272611
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OFFSET

1,1


COMMENTS

Grantham incorrectly claims that "the first Frobenius pseudoprime with respect to the Fibonacci polynomial x^2  x  1 is 5777". Crandall and Pomerance state that the first such Frobenius pseudoprime is actually 4181.
The Frobenius (1,1) pseudoprimes are a subset of the odd Fibonacci pseudoprimes A081264. Among other ways, this can be seen by Theorem 3.6.6 of Crandall and Pomerance (2005) where the Frobenius criterion with respect to x^2  Px + Q is an additional condition on an input which has passed the Lucas test for the same polynomial.  Dana Jacobsen, Aug 05 2015
Many other quadratics have a sparser set of pseudoprimes. For example, while there are 98702 pseudoprimes below 10^13 with respect to the Fibonacci polynomial, there are only 3897 for x^2  3x  5.  Dana Jacobsen, Aug 05 2015
This is the intersection of A049062 and (A081264 union A141137), that is, composite k coprime to 5 such that Fibonacci(k) == (k/5) (mod k) and that k divides Fibonacci(k(k/5)), where (k/5) is the Legendre or Jacobi symbol.  Jianing Song, Sep 12 2018


REFERENCES

R. Crandall, C. B. Pomerance. Prime Numbers: A Computational Perspective. Springer, 2nd ed., 2005.


LINKS

Amiram Eldar, Table of n, a(n) for n = 1..10000 (from Dana Jacobsen's site, terms 1..653 from Max Alekseyev)
Dorin Andrica and Ovidiu Bagdasar, Recurrent Sequences: Key Results, Applications, and Problems, Springer (2020), p. 89.
Jon Grantham, Frobenius pseudoprimes, Mathematics of Computation 70 (234): 873891, 2001. doi: 10.1090/S0025571800011972.
Dana Jacobsen, Pseudoprime Statistics, Tables, and Data (includes terms through 10^13)
A. Rotkiewicz, Lucas and Frobenius Pseudoprimes, Annales Mathematicae Silesiane, 17 (2003): 1739.
Lawrence Somer, Lucas sequences {Uk} for which U2p and Up are pseudoprimes for almost all primes p, Fibonacci Quart. 44 (2006), no. 1, 712.
Eric W. Weisstein, Frobenius Pseudoprime, MathWorld.


PROG

(PARI) { isFP(n) = if(ispseudoprime(n), return(0)); t=Mod(x*Mod(1, n), (x^2x1)*Mod(1, n))^n; (kronecker(5, n)==1 && t==1x)(kronecker(5, n)==1 && t==x) }
(Perl) use ntheory ":all"; foroddcomposites { say if is_frobenius_pseudoprime($_, 1, 1) } 1e10; # Dana Jacobsen, Aug 05 2015


CROSSREFS

Cf. A049062, A081264, A141137.
Cf. also A005845, A094063, A094395, A094411.
Terms congruent to 2 or 3 mod 5 are given in A212423.
Sequence in context: A155511 A049062 A093372 * A319168 A091982 A238082
Adjacent sequences: A212421 A212422 A212423 * A212425 A212426 A212427


KEYWORD

nonn


AUTHOR

Max Alekseyev, May 16 2012


STATUS

approved



