21728406 has 16 divisors (see below), whose sum is σ = 49665024. Its totient is φ = 6208104.

The previous prime is 21728393. The next prime is 21728407. The reversal of 21728406 is 60482712.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21728407) 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, 258630 + ... + 258713.

It is an arithmetic number, because the mean of its divisors is an integer number (3104064).

Almost surely, 2^21728406 is an apocalyptic number.

21728406 is an abundant number, since it is smaller than the sum of its proper divisors (27936618).

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

21728406 is a wasteful number, since it uses less digits than its factorization.

21728406 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 517355.

The product of its (nonzero) digits is 5376, while the sum is 30.

The square root of 21728406 is about 4661.3738318225. The cubic root of 21728406 is about 279.0460991901.

The spelling of 21728406 in words is "twenty-one million, seven hundred twenty-eight thousand, four hundred six".