21051881 has 4 divisors (see below), whose sum is σ = 21065472. Its totient is φ = 21038292.

The previous prime is 21051859. The next prime is 21051887. The reversal of 21051881 is 18815012.

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 21051881 - 2¹⁰ = 21050857 is a prime.

It is a super-2 number, since 2×21051881² = 886363387276322, which contains 22 as substring.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21051881.

It is not an unprimeable number, because it can be changed into a prime (21051887) 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, 4121 + ... + 7686.

It is an arithmetic number, because the mean of its divisors is an integer number (5266368).

Almost surely, 2^21051881 is an apocalyptic number.

It is an amenable number.

21051881 is a deficient number, since it is larger than the sum of its proper divisors (13591).

21051881 is a wasteful number, since it uses less digits than its factorization.

21051881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13590.

The product of its (nonzero) digits is 640, while the sum is 26.

The square root of 21051881 is about 4588.2328842377. The cubic root of 21051881 is about 276.1194303894.

Adding to 21051881 its reverse (18815012), we get a palindrome (39866893).

The spelling of 21051881 in words is "twenty-one million, fifty-one thousand, eight hundred eighty-one".