21542531 has 4 divisors (see below), whose sum is σ = 21603912. Its totient is φ = 21481152.

The previous prime is 21542483. The next prime is 21542537. The reversal of 21542531 is 13524512.

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 21542531 - 2¹⁴ = 21526147 is a prime.

It is a super-2 number, since 2×21542531² = 928161283771922, 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 = 21542497 and 21542506.

It is not an unprimeable number, because it can be changed into a prime (21542537) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 30161 + ... + 30866.

It is an arithmetic number, because the mean of its divisors is an integer number (5400978).

Almost surely, 2^21542531 is an apocalyptic number.

21542531 is a deficient number, since it is larger than the sum of its proper divisors (61381).

21542531 is an equidigital number, since it uses as much as digits as its factorization.

21542531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 61380.

The product of its digits is 1200, while the sum is 23.

The square root of 21542531 is about 4641.3932175587. The cubic root of 21542531 is about 278.2481222496.

It can be divided in two parts, 21 and 542531, that multiplied together give a triangular number (11393151 = T₄₇₇₃).

The spelling of 21542531 in words is "twenty-one million, five hundred forty-two thousand, five hundred thirty-one".