21233531 has 24 divisors (see below), whose sum is σ = 25084080. Its totient is φ = 17811200.

The previous prime is 21233503. The next prime is 21233579. The reversal of 21233531 is 13533212.

It is a de Polignac number, because none of the positive numbers 2^k-21233531 is a prime.

It is a super-2 number, since 2×21233531² = 901725677455922, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21233131) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 238535 + ... + 238623.

It is an arithmetic number, because the mean of its divisors is an integer number (1045170).

Almost surely, 2^21233531 is an apocalyptic number.

21233531 is a deficient number, since it is larger than the sum of its proper divisors (3850549).

21233531 is a wasteful number, since it uses less digits than its factorization.

21233531 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 187 (or 164 counting only the distinct ones).

The product of its digits is 540, while the sum is 20.

The square root of 21233531 is about 4607.9855685538. The cubic root of 21233531 is about 276.9113393391.

Adding to 21233531 its reverse (13533212), we get a palindrome (34766743).

The spelling of 21233531 in words is "twenty-one million, two hundred thirty-three thousand, five hundred thirty-one".