21442561 has 8 divisors (see below), whose sum is σ = 24548544. Its totient is φ = 18347280.

The previous prime is 21442543. The next prime is 21442591. The reversal of 21442561 is 16524412.

It is a happy number.

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

It is not a de Polignac number, because 21442561 - 2¹⁵ = 21409793 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21442501) 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, 2226 + ... + 6916.

It is an arithmetic number, because the mean of its divisors is an integer number (3068568).

Almost surely, 2^21442561 is an apocalyptic number.

It is an amenable number.

21442561 is a deficient number, since it is larger than the sum of its proper divisors (3105983).

21442561 is an equidigital number, since it uses as much as digits as its factorization.

21442561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5351.

The product of its digits is 1920, while the sum is 25.

The square root of 21442561 is about 4630.6112987380. The cubic root of 21442561 is about 277.8170431546.

Adding to 21442561 its reverse (16524412), we get a palindrome (37966973).

The spelling of 21442561 in words is "twenty-one million, four hundred forty-two thousand, five hundred sixty-one".