A number of the form obtained by setting in a Fermat-Lucas polynomial, more commonly known as a Mersenne number.
Fermat-Lucas Number
See also
Mersenne NumberExplore with Wolfram|Alpha
References
Shorey, T. N. and Stewart, C. L. "On Divisors of Fermat, Fibonacci, Lucas and Lehmer Numbers, 2." J. London Math. Soc. 23, 17-23, 1981.Stewart, C. L. "On Divisors of Fermat, Fibonacci, Lucas and Lehmer Numbers." Proc. London Math. Soc. 35, 425-447, 1977.Referenced on Wolfram|Alpha
Fermat-Lucas NumberCite this as:
Weisstein, Eric W. "Fermat-Lucas Number." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Fermat-LucasNumber.html