21847561 has 4 divisors (see below), whose sum is σ = 22173712. Its totient is φ = 21521412.

The previous prime is 21847559. The next prime is 21847571. The reversal of 21847561 is 16574812.

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 21847561 - 2¹ = 21847559 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21847531) 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, 162975 + ... + 163108.

It is an arithmetic number, because the mean of its divisors is an integer number (5543428).

Almost surely, 2^21847561 is an apocalyptic number.

It is an amenable number.

21847561 is a deficient number, since it is larger than the sum of its proper divisors (326151).

21847561 is an equidigital number, since it uses as much as digits as its factorization.

21847561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 326150.

The product of its digits is 13440, while the sum is 34.

The square root of 21847561 is about 4674.1374605375. The cubic root of 21847561 is about 279.5552505708. Note that the first 3 decimals are identical.

The spelling of 21847561 in words is "twenty-one million, eight hundred forty-seven thousand, five hundred sixty-one".