21255724 has 24 divisors (see below), whose sum is σ = 43979040. Its totient is φ = 8795136.

The previous prime is 21255721. The next prime is 21255727. The reversal of 21255724 is 42755212.

It is an interprime number because it is at equal distance from previous prime (21255721) and next prime (21255727).

It is a Harshad number since it is a multiple of its sum of digits (28).

It is a junction number, because it is equal to n+sod(n) for n = 21255692 and 21255701.

It is not an unprimeable number, because it can be changed into a prime (21255721) 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, 12277 + ... + 13900.

It is an arithmetic number, because the mean of its divisors is an integer number (1832460).

Almost surely, 2^21255724 is an apocalyptic number.

It is an amenable number.

21255724 is an abundant number, since it is smaller than the sum of its proper divisors (22723316).

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

21255724 is a wasteful number, since it uses less digits than its factorization.

21255724 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 26217 (or 26215 counting only the distinct ones).

The product of its digits is 5600, while the sum is 28.

The square root of 21255724 is about 4610.3930418132. The cubic root of 21255724 is about 277.0077804120.

The spelling of 21255724 in words is "twenty-one million, two hundred fifty-five thousand, seven hundred twenty-four".