21130561 has 4 divisors (see below), whose sum is σ = 21812224. Its totient is φ = 20448900.

The previous prime is 21130511. The next prime is 21130573. The reversal of 21130561 is 16503112.

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 21130561 - 2⁹ = 21130049 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21130511) 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, 340785 + ... + 340846.

It is an arithmetic number, because the mean of its divisors is an integer number (5453056).

Almost surely, 2^21130561 is an apocalyptic number.

It is an amenable number.

21130561 is a deficient number, since it is larger than the sum of its proper divisors (681663).

21130561 is an equidigital number, since it uses as much as digits as its factorization.

21130561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 681662.

The product of its (nonzero) digits is 180, while the sum is 19.

The square root of 21130561 is about 4596.7989949529. The cubic root of 21130561 is about 276.4629953737.

Adding to 21130561 its reverse (16503112), we get a palindrome (37633673).

The spelling of 21130561 in words is "twenty-one million, one hundred thirty thousand, five hundred sixty-one".