21445561 has 4 divisors (see below), whose sum is σ = 21765712. Its totient is φ = 21125412.

The previous prime is 21445537. The next prime is 21445573. The reversal of 21445561 is 16554412.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21445561 - 2¹³ = 21437369 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21445511) 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, 159975 + ... + 160108.

It is an arithmetic number, because the mean of its divisors is an integer number (5441428).

Almost surely, 2^21445561 is an apocalyptic number.

It is an amenable number.

21445561 is a deficient number, since it is larger than the sum of its proper divisors (320151).

21445561 is an equidigital number, since it uses as much as digits as its factorization.

21445561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 320150.

The product of its digits is 4800, while the sum is 28.

The square root of 21445561 is about 4630.9352187220. The cubic root of 21445561 is about 277.8299988872.

Adding to 21445561 its reverse (16554412), we get a palindrome (37999973).

The spelling of 21445561 in words is "twenty-one million, four hundred forty-five thousand, five hundred sixty-one".