Catalan (1876, 1891) noted that the sequence of Mersenne numbers 2^2 - 1 = 3, 2^3 - 1 = 7, and 2^7 - 1 = 127, and 2^127 - 1 = 170141183460469231731687303715884105727 (OEIS A007013) were all prime. Therefore, the numbers defined by c_n = 2^(c_(n - 1)) - 1 with c_0 = 2 are known in this work as Catalan-Mersenne numbers. It is not known if c_5 is prime, but it is known that it has no prime factor less than 10^51 (Noll; private correspondence with C. K. Caldwell, Aug. 10, 2003). c_5 appeared in the Futurama movie The Beast with a Billion Backs. The Catalan-Mersenne numbers are a subset of the double Mersenne numbers.

double Mersenne number | Mersenne number | Mersenne prime