21720337187 has 4 divisors (see below), whose sum is σ = 21720708720. Its totient is φ = 21719965656.

The previous prime is 21720337157. The next prime is 21720337207. The reversal of 21720337187 is 78173302712.

It is a happy number.

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 21720337187 - 2⁸ = 21720336931 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21720337157) 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, 76748 + ... + 222105.

It is an arithmetic number, because the mean of its divisors is an integer number (5430177180).

Almost surely, 2^21720337187 is an apocalyptic number.

21720337187 is a deficient number, since it is larger than the sum of its proper divisors (371533).

21720337187 is an equidigital number, since it uses as much as digits as its factorization.

21720337187 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 371532.

The product of its (nonzero) digits is 98784, while the sum is 41.

Adding to 21720337187 its reverse (78173302712), we get a palindrome (99893639899).

The spelling of 21720337187 in words is "twenty-one billion, seven hundred twenty million, three hundred thirty-seven thousand, one hundred eighty-seven".