21531881 has 8 divisors (see below), whose sum is σ = 24684864. Its totient is φ = 18398160.

The previous prime is 21531871. The next prime is 21531889. The reversal of 21531881 is 18813512.

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

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21531881 is a prime.

It is a super-2 number, since 2×21531881² = 927243798796322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21531889) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 2330 + ... + 6963.

It is an arithmetic number, because the mean of its divisors is an integer number (3085608).

Almost surely, 2^21531881 is an apocalyptic number.

It is an amenable number.

21531881 is a deficient number, since it is larger than the sum of its proper divisors (3152983).

21531881 is an equidigital number, since it uses as much as digits as its factorization.

21531881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9631.

The product of its digits is 1920, while the sum is 29.

The square root of 21531881 is about 4640.2457909038. The cubic root of 21531881 is about 278.2022621018.

The spelling of 21531881 in words is "twenty-one million, five hundred thirty-one thousand, eight hundred eighty-one".