21209178206 has 32 divisors (see below), whose sum is σ = 34304599008. Its totient is φ = 9797898240.

The previous prime is 21209178187. The next prime is 21209178251. The reversal of 21209178206 is 60287190212.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 21209178206.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 1074926 + ... + 1094478.

It is an arithmetic number, because the mean of its divisors is an integer number (1072018719).

Almost surely, 2^21209178206 is an apocalyptic number.

21209178206 is a deficient number, since it is larger than the sum of its proper divisors (13095420802).

21209178206 is a wasteful number, since it uses less digits than its factorization.

21209178206 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 20156.

The product of its (nonzero) digits is 24192, while the sum is 38.

The spelling of 21209178206 in words is "twenty-one billion, two hundred nine million, one hundred seventy-eight thousand, two hundred six".