21542731 has 4 divisors (see below), whose sum is σ = 24620272. Its totient is φ = 18465192.

The previous prime is 21542687. The next prime is 21542761. The reversal of 21542731 is 13724512.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21542731 - 2¹⁵ = 21509963 is a prime.

It is a super-2 number, since 2×21542731² = 928178517876722, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21542696 and 21542705.

It is not an unprimeable number, because it can be changed into a prime (21542761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1538760 + ... + 1538773.

It is an arithmetic number, because the mean of its divisors is an integer number (6155068).

Almost surely, 2^21542731 is an apocalyptic number.

21542731 is a deficient number, since it is larger than the sum of its proper divisors (3077541).

21542731 is an equidigital number, since it uses as much as digits as its factorization.

21542731 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3077540.

The product of its digits is 1680, while the sum is 25.

The square root of 21542731 is about 4641.4147627636. The cubic root of 21542731 is about 278.2489833284.

The spelling of 21542731 in words is "twenty-one million, five hundred forty-two thousand, seven hundred thirty-one".