21008885731 has 4 divisors (see below), whose sum is σ = 21364968600. Its totient is φ = 20652802864.

The previous prime is 21008885701. The next prime is 21008885741. The reversal of 21008885731 is 13758880012.

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 21008885731 - 2¹⁹ = 21008361443 is a prime.

It is a super-2 number, since 2×21008885731² (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 (21008885701) 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, 178041346 + ... + 178041463.

It is an arithmetic number, because the mean of its divisors is an integer number (5341242150).

Almost surely, 2^21008885731 is an apocalyptic number.

21008885731 is a deficient number, since it is larger than the sum of its proper divisors (356082869).

21008885731 is an equidigital number, since it uses as much as digits as its factorization.

21008885731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 356082868.

The product of its (nonzero) digits is 107520, while the sum is 43.

The spelling of 21008885731 in words is "twenty-one billion, eight million, eight hundred eighty-five thousand, seven hundred thirty-one".