21715218 has 24 divisors (see below), whose sum is σ = 53771328. Its totient is φ = 6204312.

The previous prime is 21715217. The next prime is 21715219. The reversal of 21715218 is 81251712.

It is an interprime number because it is at equal distance from previous prime (21715217) and next prime (21715219).

It is a junction number, because it is equal to n+sod(n) for n = 21715191 and 21715200.

It is not an unprimeable number, because it can be changed into a prime (21715217) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 86046 + ... + 86297.

It is an arithmetic number, because the mean of its divisors is an integer number (2240472).

Almost surely, 2^21715218 is an apocalyptic number.

21715218 is an abundant number, since it is smaller than the sum of its proper divisors (32056110).

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

21715218 is a wasteful number, since it uses less digits than its factorization.

21715218 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 172358 (or 172355 counting only the distinct ones).

The product of its digits is 1120, while the sum is 27.

The square root of 21715218 is about 4659.9590126953. The cubic root of 21715218 is about 278.9896323276.

The spelling of 21715218 in words is "twenty-one million, seven hundred fifteen thousand, two hundred eighteen".