21717618 has 32 divisors (see below), whose sum is σ = 47924352. Its totient is φ = 6518400.

The previous prime is 21717617. The next prime is 21717629. The reversal of 21717618 is 81671712.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21717613) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 198 + ... + 6593.

It is an arithmetic number, because the mean of its divisors is an integer number (1497636).

Almost surely, 2^21717618 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21717618, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (23962176).

21717618 is an abundant number, since it is smaller than the sum of its proper divisors (26206734).

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

21717618 is a wasteful number, since it uses less digits than its factorization.

21717618 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6850.

The product of its digits is 4704, while the sum is 33.

The square root of 21717618 is about 4660.2165185751. The cubic root of 21717618 is about 278.9999100731. Note that the first 4 decimals are identical.

The spelling of 21717618 in words is "twenty-one million, seven hundred seventeen thousand, six hundred eighteen".