21397991481 has 16 divisors (see below), whose sum is σ = 31707808000. Its totient is φ = 14262141744.

The previous prime is 21397991453. The next prime is 21397991491. The reversal of 21397991481 is 18419979312.

21397991481 is a `hidden beast` number, since 2 + 1 + 3 + 9 + 79 + 91 + 481 = 666.

It is not a de Polignac number, because 21397991481 - 2⁵ = 21397991449 is a prime.

It is a super-2 number, since 2×21397991481² (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 (21397991491) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 37920 + ... + 210318.

It is an arithmetic number, because the mean of its divisors is an integer number (1981738000).

Almost surely, 2^21397991481 is an apocalyptic number.

It is an amenable number.

21397991481 is a deficient number, since it is larger than the sum of its proper divisors (10309816519).

21397991481 is a wasteful number, since it uses less digits than its factorization.

21397991481 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 177005 (or 176999 counting only the distinct ones).

The product of its digits is 979776, while the sum is 54.

The spelling of 21397991481 in words is "twenty-one billion, three hundred ninety-seven million, nine hundred ninety-one thousand, four hundred eighty-one".