21745218 has 16 divisors (see below), whose sum is σ = 47444256. Its totient is φ = 6589440.

The previous prime is 21745201. The next prime is 21745247. The reversal of 21745218 is 81254712.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 164671 + ... + 164802.

It is an arithmetic number, because the mean of its divisors is an integer number (2965266).

Almost surely, 2^21745218 is an apocalyptic number.

21745218 is an abundant number, since it is smaller than the sum of its proper divisors (25699038).

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

21745218 is a wasteful number, since it uses less digits than its factorization.

21745218 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 329489.

The product of its digits is 4480, while the sum is 30.

The square root of 21745218 is about 4663.1768141472. The cubic root of 21745218 is about 279.1180497601.

It can be divided in two parts, 217452 and 18, that added together give a triangular number (217470 = T₆₅₉).

The spelling of 21745218 in words is "twenty-one million, seven hundred forty-five thousand, two hundred eighteen".