This number is believed to be the only odd untouchable number.
This number is believed to be the only odd untouchable number. Along with six, this number makes up the first Ruth-Aaron pair, in which the sums of the prime factors of each number in the pair are equal.. Niels Henrik Abel showed that there is no general algebraic solution to find the roots of polynomials of this degree or higher. This is also the first safe prime and the second Fermat prime. Additionally, this is the number of Platonic solids that exist. Along with one, this is the only number to be for which the nth term of the Fibonacci sequence is equal to n. Name this number, the base of the quinary number system and the number of sides of a pentagon.
This number is believed to be the only odd untouchable number.
{five }