21842561 has 8 divisors (see below), whose sum is σ = 23732520. Its totient is φ = 19982592.

The previous prime is 21842551. The next prime is 21842573. The reversal of 21842561 is 16524812.

It can be written as a sum of positive squares in 4 ways, for example, as 1547536 + 20295025 = 1244^2 + 4505^2 .

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

It is a cyclic number.

It is not a de Polignac number, because 21842561 - 2⁶ = 21842497 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21842521) 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, 5966 + ... + 8903.

It is an arithmetic number, because the mean of its divisors is an integer number (2966565).

Almost surely, 2^21842561 is an apocalyptic number.

It is an amenable number.

21842561 is a deficient number, since it is larger than the sum of its proper divisors (1889959).

21842561 is a wasteful number, since it uses less digits than its factorization.

21842561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 14995.

The product of its digits is 3840, while the sum is 29.

The square root of 21842561 is about 4673.6025718925. The cubic root of 21842561 is about 279.5339227454.

The spelling of 21842561 in words is "twenty-one million, eight hundred forty-two thousand, five hundred sixty-one".