21724731 has 24 divisors (see below), whose sum is σ = 35992320. Its totient is φ = 12369456.

The previous prime is 21724721. The next prime is 21724739. The reversal of 21724731 is 13742712.

It is a happy number.

It is not a de Polignac number, because 21724731 - 2¹⁴ = 21708347 is a prime.

It is a super-2 number, since 2×21724731² = 943927874044722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21724695 and 21724704.

It is not an unprimeable number, because it can be changed into a prime (21724739) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 25986 + ... + 26808.

It is an arithmetic number, because the mean of its divisors is an integer number (1499680).

Almost surely, 2^21724731 is an apocalyptic number.

21724731 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21724731 is a deficient number, since it is larger than the sum of its proper divisors (14267589).

21724731 is a wasteful number, since it uses less digits than its factorization.

21724731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1255 (or 1252 counting only the distinct ones).

The product of its digits is 2352, while the sum is 27.

The square root of 21724731 is about 4660.9796180631. The cubic root of 21724731 is about 279.0303662944.

It can be divided in two parts, 2172 and 4731, that added together give a triangular number (6903 = T₁₁₇).

The spelling of 21724731 in words is "twenty-one million, seven hundred twenty-four thousand, seven hundred thirty-one".