21302561 has 4 divisors (see below), whose sum is σ = 24345792. Its totient is φ = 18259332.

The previous prime is 21302557. The next prime is 21302569. The reversal of 21302561 is 16520312.

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 not a de Polignac number, because 21302561 - 2² = 21302557 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21302569) 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, 1521605 + ... + 1521618.

It is an arithmetic number, because the mean of its divisors is an integer number (6086448).

Almost surely, 2^21302561 is an apocalyptic number.

It is an amenable number.

21302561 is a deficient number, since it is larger than the sum of its proper divisors (3043231).

21302561 is an equidigital number, since it uses as much as digits as its factorization.

21302561 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3043230.

The product of its (nonzero) digits is 360, while the sum is 20.

The square root of 21302561 is about 4615.4697485738. The cubic root of 21302561 is about 277.2110934192.

Adding to 21302561 its reverse (16520312), we get a palindrome (37822873).

The spelling of 21302561 in words is "twenty-one million, three hundred two thousand, five hundred sixty-one".