21423731 has 6 divisors (see below), whose sum is σ = 24921540. Its totient is φ = 18363156.

The previous prime is 21423709. The next prime is 21423751. The reversal of 21423731 is 13732412.

It is not a de Polignac number, because 21423731 - 2¹⁰ = 21422707 is a prime.

It is a super-2 number, since 2×21423731² = 917952499920722, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21423697 and 21423706.

It is not an unprimeable number, because it can be changed into a prime (21423751) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 218561 + ... + 218658.

It is an arithmetic number, because the mean of its divisors is an integer number (4153590).

Almost surely, 2^21423731 is an apocalyptic number.

21423731 is a deficient number, since it is larger than the sum of its proper divisors (3497809).

21423731 is an equidigital number, since it uses as much as digits as its factorization.

21423731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 437233 (or 437226 counting only the distinct ones).

The product of its digits is 1008, while the sum is 23.

The square root of 21423731 is about 4628.5776432939. The cubic root of 21423731 is about 277.7356967306.

The spelling of 21423731 in words is "twenty-one million, four hundred twenty-three thousand, seven hundred thirty-one".