OFFSET
1,1
COMMENTS
These numbers may be called weak generalized Fibonacci-Lucas-Bruckner pseudoprimes.
If p is a prime, then F(p)^2 == 1 (mod p) and L(p) == 1 (mod p).
This sequence contains the odd composite integers for which these congruences hold.
For a,b integers, the following sequences are defined:
generalized Lucas sequences by U(n+2)=a*U(n+1)-b*U(n) and U(0)=0, U(1)=1,
generalized Pell-Lucas sequences by V(n+2)=a*V(n+1)-b*V(n) and V(0)=2, V(1)=a.
These satisfy the identities U(p)^2 == 1 and V(p)==a (mod p) for p prime and b=1,-1.
These numbers may be called weak generalized Lucas-Bruckner pseudoprimes of parameters a and b.The current sequence is defined for a=1 and b=-1.
Examples: a(n) is also the number of Jones graphs on n nodes.
LINKS
Dorin Andrica and Ovidiu Bagdasar, On some new arithmetic properties of the generalized Lucas sequences, Mediterr. J. Math., 18 (2021), 47.
MATHEMATICA
Select[Range[3, 20000, 2], CompositeQ[#] && Divisible[Fibonacci[#, 1]*Fibonacci[#, 1] - 1, #] && Divisible[LucasL[#, 1] - 1, #] &]
CROSSREFS
KEYWORD
nonn
AUTHOR
Ovidiu Bagdasar, Sep 19 2020
EXTENSIONS
More terms from Amiram Eldar, Sep 19 2020
STATUS
approved