21605718 has 24 divisors (see below), whose sum is σ = 43767144. Its totient is φ = 7110400.

The previous prime is 21605711. The next prime is 21605747. The reversal of 21605718 is 81750612.

21605718 is nontrivially palindromic in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21605711) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 61030 + ... + 61382.

It is an arithmetic number, because the mean of its divisors is an integer number (1823631).

Almost surely, 2^21605718 is an apocalyptic number.

21605718 is an abundant number, since it is smaller than the sum of its proper divisors (22161426).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21605718 is a wasteful number, since it uses less digits than its factorization.

21605718 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 560 (or 459 counting only the distinct ones).

The product of its (nonzero) digits is 3360, while the sum is 30.

The square root of 21605718 is about 4648.1951335976. The cubic root of 21605718 is about 278.5199024828.

The spelling of 21605718 in words is "twenty-one million, six hundred five thousand, seven hundred eighteen".