21918388 has 6 divisors (see below), whose sum is σ = 38357186. Its totient is φ = 10959192.

The previous prime is 21918367. The next prime is 21918397. The reversal of 21918388 is 88381912.

It can be written as a sum of positive squares in only one way, i.e., 21790224 + 128164 = 4668^2 + 358^2 .

It is a self number, because there is not a number n which added to its sum of digits gives 21918388.

It is a congruent number.

It is an unprimeable number.

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 as a sum of consecutive naturals, namely, 2739795 + ... + 2739802.

Almost surely, 2^21918388 is an apocalyptic number.

It is an amenable number.

21918388 is a deficient number, since it is larger than the sum of its proper divisors (16438798).

21918388 is a wasteful number, since it uses less digits than its factorization.

21918388 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5479601 (or 5479599 counting only the distinct ones).

The product of its digits is 27648, while the sum is 40.

The square root of 21918388 is about 4681.7078080547. The cubic root of 21918388 is about 279.8570188363.

The spelling of 21918388 in words is "twenty-one million, nine hundred eighteen thousand, three hundred eighty-eight".