21397918731 has 48 divisors (see below), whose sum is σ = 35748028800. Its totient is φ = 11314380672.

The previous prime is 21397918691. The next prime is 21397918747. The reversal of 21397918731 is 13781979312.

It is not a de Polignac number, because 21397918731 - 2⁹ = 21397918219 is a prime.

It is a super-2 number, since 2×21397918731² (a number of 21 digits) contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21397918781) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 31015 + ... + 209183.

It is an arithmetic number, because the mean of its divisors is an integer number (744750600).

Almost surely, 2^21397918731 is an apocalyptic number.

21397918731 is a gapful number since it is divisible by the number (21) formed by its first and last digit.

21397918731 is a deficient number, since it is larger than the sum of its proper divisors (14350110069).

21397918731 is a wasteful number, since it uses less digits than its factorization.

21397918731 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 178248 (or 178241 counting only the distinct ones).

The product of its digits is 571536, while the sum is 51.

The spelling of 21397918731 in words is "twenty-one billion, three hundred ninety-seven million, nine hundred eighteen thousand, seven hundred thirty-one".