21664020371 has 4 divisors (see below), whose sum is σ = 24758880432. Its totient is φ = 18569160312.

The previous prime is 21664020347. The next prime is 21664020379. The reversal of 21664020371 is 17302046612.

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 21664020371 - 2¹⁴ = 21664003987 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21664020379) 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, 1547430020 + ... + 1547430033.

It is an arithmetic number, because the mean of its divisors is an integer number (6189720108).

Almost surely, 2^21664020371 is an apocalyptic number.

21664020371 is a deficient number, since it is larger than the sum of its proper divisors (3094860061).

21664020371 is an equidigital number, since it uses as much as digits as its factorization.

21664020371 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3094860060.

The product of its (nonzero) digits is 12096, while the sum is 32.

Adding to 21664020371 its reverse (17302046612), we get a palindrome (38966066983).

The spelling of 21664020371 in words is "twenty-one billion, six hundred sixty-four million, twenty thousand, three hundred seventy-one".