Re:binary (Score 2, Informative)

2 (as per usual) is a special case. 5 and 13 aren't mersenne numbers and therefore aren't in the list. Those numbers are the "exponent" as in 2 to the power of 5 minus 1 = 31 and 2 to the power of 13 minus 1 = 8191 are both mersenne primes and are both strings of 1 in binary.