21157717523 has 4 divisors (see below), whose sum is σ = 22402289160. Its totient is φ = 19913145888.

The previous prime is 21157717487. The next prime is 21157717579. The reversal of 21157717523 is 32571775112.

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 21157717523 - 2⁸ = 21157717267 is a prime.

It is a super-2 number, since 2×21157717523² (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 (21157717223) 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, 622285793 + ... + 622285826.

It is an arithmetic number, because the mean of its divisors is an integer number (5600572290).

Almost surely, 2^21157717523 is an apocalyptic number.

21157717523 is a deficient number, since it is larger than the sum of its proper divisors (1244571637).

21157717523 is a wasteful number, since it uses less digits than its factorization.

21157717523 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1244571636.

The product of its digits is 102900, while the sum is 41.

The spelling of 21157717523 in words is "twenty-one billion, one hundred fifty-seven million, seven hundred seventeen thousand, five hundred twenty-three".