21188681 has 16 divisors (see below), whose sum is σ = 23929344. Its totient is φ = 18653184.

The previous prime is 21188659. The next prime is 21188693. The reversal of 21188681 is 18688112.

It is not a de Polignac number, because 21188681 - 2⁶ = 21188617 is a prime.

It is a super-2 number, since 2×21188681² = 897920405039522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21188621) 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, 17801 + ... + 18953.

It is an arithmetic number, because the mean of its divisors is an integer number (1495584).

Almost surely, 2^21188681 is an apocalyptic number.

It is an amenable number.

21188681 is a deficient number, since it is larger than the sum of its proper divisors (2740663).

21188681 is a wasteful number, since it uses less digits than its factorization.

21188681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1240.

The product of its digits is 6144, while the sum is 35.

The square root of 21188681 is about 4603.1164443233. The cubic root of 21188681 is about 276.7162355339.

The spelling of 21188681 in words is "twenty-one million, one hundred eighty-eight thousand, six hundred eighty-one".