21222531 has 18 divisors (see below), whose sum is σ = 33513948. Its totient is φ = 12834360.

The previous prime is 21222529. The next prime is 21222557. The reversal of 21222531 is 13522212.

It is not a de Polignac number, because 21222531 - 2¹ = 21222529 is a prime.

It is a super-2 number, since 2×21222531² = 900791644091922, which contains 22 as substring.

It is a hoax number, since the sum of its digits (18) coincides with the sum of the digits of its distinct prime factors.

It is not an unprimeable number, because it can be changed into a prime (21222931) 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 17 ways as a sum of consecutive naturals, for example, 45606 + ... + 46068.

It is an arithmetic number, because the mean of its divisors is an integer number (1861886).

Almost surely, 2^21222531 is an apocalyptic number.

21222531 is a deficient number, since it is larger than the sum of its proper divisors (12291417).

21222531 is an equidigital number, since it uses as much as digits as its factorization.

21222531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 943 (or 477 counting only the distinct ones).

The product of its digits is 240, while the sum is 18.

The square root of 21222531 is about 4606.7918338037. The cubic root of 21222531 is about 276.8635132399.

Adding to 21222531 its reverse (13522212), we get a palindrome (34744743).

The spelling of 21222531 in words is "twenty-one million, two hundred twenty-two thousand, five hundred thirty-one".