21561881 has 8 divisors (see below), whose sum is σ = 23587200. Its totient is φ = 19547440.

The previous prime is 21561851. The next prime is 21561887. The reversal of 21561881 is 18816512.

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

It is not a de Polignac number, because 21561881 - 2⁶ = 21561817 is a prime.

It is a super-2 number, since 2×21561881² = 929829424516322, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (21561887) 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, 1760 + ... + 6798.

It is an arithmetic number, because the mean of its divisors is an integer number (2948400).

Almost surely, 2^21561881 is an apocalyptic number.

It is an amenable number.

21561881 is a deficient number, since it is larger than the sum of its proper divisors (2025319).

21561881 is a wasteful number, since it uses less digits than its factorization.

21561881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5439.

The product of its digits is 3840, while the sum is 32.

The square root of 21561881 is about 4643.4772530938. The cubic root of 21561881 is about 278.3314069532.

The spelling of 21561881 in words is "twenty-one million, five hundred sixty-one thousand, eight hundred eighty-one".