21180561 has 4 divisors (see below), whose sum is σ = 28240752. Its totient is φ = 14120372.

The previous prime is 21180529. The next prime is 21180571. The reversal of 21180561 is 16508112.

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 21180561 - 2⁵ = 21180529 is a prime.

It is not an unprimeable number, because it can be changed into a prime (21180571) 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, 3530091 + ... + 3530096.

It is an arithmetic number, because the mean of its divisors is an integer number (7060188).

Almost surely, 2^21180561 is an apocalyptic number.

It is an amenable number.

21180561 is a deficient number, since it is larger than the sum of its proper divisors (7060191).

21180561 is an equidigital number, since it uses as much as digits as its factorization.

21180561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7060190.

The product of its (nonzero) digits is 480, while the sum is 24.

The square root of 21180561 is about 4602.2343486615. The cubic root of 21180561 is about 276.6808829649.

Adding to 21180561 its reverse (16508112), we get a palindrome (37688673).

The spelling of 21180561 in words is "twenty-one million, one hundred eighty thousand, five hundred sixty-one".