21255531 has 8 divisors (see below), whose sum is σ = 30917184. Its totient is φ = 12882120.

The previous prime is 21255529. The next prime is 21255541. The reversal of 21255531 is 13555212.

It is a happy number.

It is a sphenic number, since it is the product of 3 distinct primes.

It is not a de Polignac number, because 21255531 - 2¹ = 21255529 is a prime.

It is a super-2 number, since 2×21255531² = 903595196183922, which contains 22 as substring.

It is a plaindrome in base 16.

It is not an unprimeable number, because it can be changed into a prime (21255541) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 322021 + ... + 322086.

It is an arithmetic number, because the mean of its divisors is an integer number (3864648).

Almost surely, 2^21255531 is an apocalyptic number.

21255531 is a deficient number, since it is larger than the sum of its proper divisors (9661653).

21255531 is a wasteful number, since it uses less digits than its factorization.

21255531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 644121.

The product of its digits is 1500, while the sum is 24.

The square root of 21255531 is about 4610.3721107954. The cubic root of 21255531 is about 277.0069420078.

It can be divided in two parts, 21 and 255531, that added together give a palindrome (255552).

The spelling of 21255531 in words is "twenty-one million, two hundred fifty-five thousand, five hundred thirty-one".