21388881 has 8 divisors (see below), whose sum is σ = 28664064. Its totient is φ = 14186480.

The previous prime is 21388867. The next prime is 21388883. The reversal of 21388881 is 18888312.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21388881 - 2¹⁷ = 21257809 is a prime.

It is a super-2 number, since 2×21388881² = 914968460864322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21388883) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 17505 + ... + 18686.

It is an arithmetic number, because the mean of its divisors is an integer number (3583008).

Almost surely, 2^21388881 is an apocalyptic number.

It is an amenable number.

21388881 is a deficient number, since it is larger than the sum of its proper divisors (7275183).

21388881 is a wasteful number, since it uses less digits than its factorization.

21388881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36391.

The product of its digits is 24576, while the sum is 39.

The square root of 21388881 is about 4624.8114556163. The cubic root of 21388881 is about 277.5850173725.

The spelling of 21388881 in words is "twenty-one million, three hundred eighty-eight thousand, eight hundred eighty-one".