21731518 has 4 divisors (see below), whose sum is σ = 32597280. Its totient is φ = 10865758.

The previous prime is 21731509. The next prime is 21731519. The reversal of 21731518 is 81513712.

It is a semiprime because it is the product of two primes.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21731519) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 5432878 + ... + 5432881.

It is an arithmetic number, because the mean of its divisors is an integer number (8149320).

Almost surely, 2^21731518 is an apocalyptic number.

21731518 is a deficient number, since it is larger than the sum of its proper divisors (10865762).

21731518 is a wasteful number, since it uses less digits than its factorization.

21731518 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10865761.

The product of its digits is 1680, while the sum is 28.

The square root of 21731518 is about 4661.7076270397. The cubic root of 21731518 is about 279.0594204619.

The spelling of 21731518 in words is "twenty-one million, seven hundred thirty-one thousand, five hundred eighteen".