21157694657 has 4 divisors (see below), whose sum is σ = 23081121456. Its totient is φ = 19234267860.

The previous prime is 21157694651. The next prime is 21157694659. The reversal of 21157694657 is 75649675112.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21157694657 - 2³² = 16862727361 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21157694599 and 21157694608.

It is not an unprimeable number, because it can be changed into a prime (21157694651) 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, 961713383 + ... + 961713404.

It is an arithmetic number, because the mean of its divisors is an integer number (5770280364).

Almost surely, 2^21157694657 is an apocalyptic number.

It is an amenable number.

21157694657 is a deficient number, since it is larger than the sum of its proper divisors (1923426799).

21157694657 is a wasteful number, since it uses less digits than its factorization.

21157694657 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1923426798.

The product of its digits is 3175200, while the sum is 53.

The spelling of 21157694657 in words is "twenty-one billion, one hundred fifty-seven million, six hundred ninety-four thousand, six hundred fifty-seven".