21445531 has 4 divisors (see below), whose sum is σ = 21454992. Its totient is φ = 21436072.

The previous prime is 21445513. The next prime is 21445537. The reversal of 21445531 is 13554412.

It is a happy number.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21445531 - 2¹¹ = 21443483 is a prime.

It is a super-2 number, since 2×21445531² = 919821599743922, which contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21445496 and 21445505.

It is not an unprimeable number, because it can be changed into a prime (21445537) 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, 921 + ... + 6613.

It is an arithmetic number, because the mean of its divisors is an integer number (5363748).

Almost surely, 2^21445531 is an apocalyptic number.

21445531 is a deficient number, since it is larger than the sum of its proper divisors (9461).

21445531 is an equidigital number, since it uses as much as digits as its factorization.

21445531 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9460.

The product of its digits is 2400, while the sum is 25.

The square root of 21445531 is about 4630.9319796343. The cubic root of 21445531 is about 277.8298693359.

Adding to 21445531 its reverse (13554412), we get a palindrome (34999943).

The spelling of 21445531 in words is "twenty-one million, four hundred forty-five thousand, five hundred thirty-one".