21645005321 has 4 divisors (see below), whose sum is σ = 21647884692. Its totient is φ = 21642125952.

The previous prime is 21645005303. The next prime is 21645005341. The reversal of 21645005321 is 12350054612.

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

It can be written as a sum of positive squares in 2 ways, for example, as 4833030400 + 16811974921 = 69520^2 + 129661^2 .

It is a cyclic number.

It is not a de Polignac number, because 21645005321 - 2¹⁸ = 21644743177 is a prime.

It is a super-2 number, since 2×21645005321² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21645005341) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1428380 + ... + 1443453.

It is an arithmetic number, because the mean of its divisors is an integer number (5411971173).

Almost surely, 2^21645005321 is an apocalyptic number.

It is an amenable number.

21645005321 is a deficient number, since it is larger than the sum of its proper divisors (2879371).

21645005321 is an equidigital number, since it uses as much as digits as its factorization.

21645005321 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2879370.

The product of its (nonzero) digits is 7200, while the sum is 29.

Adding to 21645005321 its reverse (12350054612), we get a palindrome (33995059933).

The spelling of 21645005321 in words is "twenty-one billion, six hundred forty-five million, five thousand, three hundred twenty-one".