21723906 has 16 divisors (see below), whose sum is σ = 43546464. Its totient is φ = 7224864.

The previous prime is 21723883. The next prime is 21723907. The reversal of 21723906 is 60932712.

It is not an unprimeable number, because it can be changed into a prime (21723907) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 1075 + ... + 6678.

It is an arithmetic number, because the mean of its divisors is an integer number (2721654).

Almost surely, 2^21723906 is an apocalyptic number.

21723906 is an abundant number, since it is smaller than the sum of its proper divisors (21822558).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21723906 is a wasteful number, since it uses less digits than its factorization.

21723906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8225.

The product of its (nonzero) digits is 4536, while the sum is 30.

The square root of 21723906 is about 4660.8911165141. The cubic root of 21723906 is about 279.0268341760.

Adding to 21723906 its sum of digits (30), we get a triangular number (21723936 = T₆₅₉₁).

The spelling of 21723906 in words is "twenty-one million, seven hundred twenty-three thousand, nine hundred six".