21561307 has 4 divisors (see below), whose sum is σ = 21585256. Its totient is φ = 21537360.

The previous prime is 21561277. The next prime is 21561311. The reversal of 21561307 is 70316512.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21561307 - 2⁷ = 21561179 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21561347) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10569 + ... + 12442.

It is an arithmetic number, because the mean of its divisors is an integer number (5396314).

Almost surely, 2^21561307 is an apocalyptic number.

21561307 is a deficient number, since it is larger than the sum of its proper divisors (23949).

21561307 is an equidigital number, since it uses as much as digits as its factorization.

21561307 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23948.

The product of its (nonzero) digits is 1260, while the sum is 25.

The square root of 21561307 is about 4643.4154455530. The cubic root of 21561307 is about 278.3289371061.

Adding to 21561307 its reverse (70316512), we get a palindrome (91877819).

The spelling of 21561307 in words is "twenty-one million, five hundred sixty-one thousand, three hundred seven".