21643544513 has 4 divisors (see below), whose sum is σ = 21647135700. Its totient is φ = 21639953328.

The previous prime is 21643544491. The next prime is 21643544557. The reversal of 21643544513 is 31544534612.

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 1356669889 + 20286874624 = 36833^2 + 142432^2 .

It is a cyclic number.

It is not a de Polignac number, because 21643544513 - 2¹² = 21643540417 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21643544113) 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, 1786538 + ... + 1798611.

It is an arithmetic number, because the mean of its divisors is an integer number (5411783925).

Almost surely, 2^21643544513 is an apocalyptic number.

It is an amenable number.

21643544513 is a deficient number, since it is larger than the sum of its proper divisors (3591187).

21643544513 is an equidigital number, since it uses as much as digits as its factorization.

21643544513 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3591186.

The product of its digits is 172800, while the sum is 38.

Subtracting 21643544513 from its reverse (31544534612), we obtain a palindrome (9900990099).

The spelling of 21643544513 in words is "twenty-one billion, six hundred forty-three million, five hundred forty-four thousand, five hundred thirteen".