21253531 has 8 divisors (see below), whose sum is σ = 23116464. Its totient is φ = 19423200.

The previous prime is 21253523. The next prime is 21253537. The reversal of 21253531 is 13535212.

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

It is a cyclic number.

It is not a de Polignac number, because 21253531 - 2³ = 21253523 is a prime.

It is a super-2 number, since 2×21253531² = 903425159935922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21253537) 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, 6781 + ... + 9406.

It is an arithmetic number, because the mean of its divisors is an integer number (2889558).

Almost surely, 2^21253531 is an apocalyptic number.

21253531 is a deficient number, since it is larger than the sum of its proper divisors (1862933).

21253531 is a wasteful number, since it uses less digits than its factorization.

21253531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 16301.

The product of its digits is 900, while the sum is 22.

The square root of 21253531 is about 4610.1552034612. The cubic root of 21253531 is about 276.9982535828.

Adding to 21253531 its reverse (13535212), we get a palindrome (34788743).

The spelling of 21253531 in words is "twenty-one million, two hundred fifty-three thousand, five hundred thirty-one".