21088531 has 4 divisors (see below), whose sum is σ = 21197992. Its totient is φ = 20979072.

The previous prime is 21088519. The next prime is 21088549. The reversal of 21088531 is 13588012.

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 21088531 - 2¹⁵ = 21055763 is a prime.

It is a super-2 number, since 2×21088531² = 889452279475922, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21088531.

It is not an unprimeable number, because it can be changed into a prime (21085531) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 54441 + ... + 54826.

It is an arithmetic number, because the mean of its divisors is an integer number (5299498).

Almost surely, 2^21088531 is an apocalyptic number.

21088531 is a deficient number, since it is larger than the sum of its proper divisors (109461).

21088531 is a wasteful number, since it uses less digits than its factorization.

21088531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 109460.

The product of its (nonzero) digits is 1920, while the sum is 28.

The square root of 21088531 is about 4592.2250598158. The cubic root of 21088531 is about 276.2795730098.

The spelling of 21088531 in words is "twenty-one million, eighty-eight thousand, five hundred thirty-one".