21756881 has 4 divisors (see below), whose sum is σ = 22902000. Its totient is φ = 20611764.

The previous prime is 21756863. The next prime is 21756883. The reversal of 21756881 is 18865712.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 21756881 - 2²² = 17562577 is a prime.

It is a super-2 number, since 2×21756881² = 946723741696322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21756883) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 572531 + ... + 572568.

It is an arithmetic number, because the mean of its divisors is an integer number (5725500).

Almost surely, 2^21756881 is an apocalyptic number.

It is an amenable number.

21756881 is a deficient number, since it is larger than the sum of its proper divisors (1145119).

21756881 is a wasteful number, since it uses less digits than its factorization.

21756881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1145118.

The product of its digits is 26880, while the sum is 38.

The square root of 21756881 is about 4664.4271888411. The cubic root of 21756881 is about 279.1679422926.

The spelling of 21756881 in words is "twenty-one million, seven hundred fifty-six thousand, eight hundred eighty-one".