21090881 has 16 divisors (see below), whose sum is σ = 25202688. Its totient is φ = 17269200.

The previous prime is 21090871. The next prime is 21090889. The reversal of 21090881 is 18809012.

It is a cyclic number.

It is not a de Polignac number, because 21090881 - 2¹⁰ = 21089857 is a prime.

It is a super-2 number, since 2×21090881² = 889650522712322, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (21090889) 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, 17426 + ... + 18596.

It is an arithmetic number, because the mean of its divisors is an integer number (1575168).

Almost surely, 2^21090881 is an apocalyptic number.

It is an amenable number.

21090881 is a deficient number, since it is larger than the sum of its proper divisors (4111807).

21090881 is a wasteful number, since it uses less digits than its factorization.

21090881 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1292.

The product of its (nonzero) digits is 1152, while the sum is 29.

The square root of 21090881 is about 4592.4809199386. The cubic root of 21090881 is about 276.2898350314.

Adding to 21090881 its reverse (18809012), we get a palindrome (39899893).

The spelling of 21090881 in words is "twenty-one million, ninety thousand, eight hundred eighty-one".