21209805812 has 24 divisors (see below), whose sum is σ = 42323641416. Its totient is φ = 9213308928.

The previous prime is 21209805797. The next prime is 21209805821. The reversal of 21209805812 is 21850890212.

It can be written as a sum of positive squares in 4 ways, for example, as 8178670096 + 13031135716 = 90436^2 + 114154^2 .

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 11995613 + ... + 11997380.

It is an arithmetic number, because the mean of its divisors is an integer number (1763485059).

Almost surely, 2^21209805812 is an apocalyptic number.

It is an amenable number.

21209805812 is a deficient number, since it is larger than the sum of its proper divisors (21113835604).

21209805812 is a wasteful number, since it uses less digits than its factorization.

21209805812 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 23993027 (or 23993025 counting only the distinct ones).

The product of its (nonzero) digits is 23040, while the sum is 38.

The spelling of 21209805812 in words is "twenty-one billion, two hundred nine million, eight hundred five thousand, eight hundred twelve".