21008881 has 4 divisors (see below), whose sum is σ = 21018352. Its totient is φ = 20999412.

The previous prime is 21008879. The next prime is 21008887. The reversal of 21008881 is 18880012.

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, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21008881 - 2¹ = 21008879 is a prime.

It is a super-2 number, since 2×21008881² = 882746161744322, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (21008887) 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, 586 + ... + 6508.

It is an arithmetic number, because the mean of its divisors is an integer number (5254588).

Almost surely, 2^21008881 is an apocalyptic number.

It is an amenable number.

21008881 is a deficient number, since it is larger than the sum of its proper divisors (9471).

21008881 is an equidigital number, since it uses as much as digits as its factorization.

21008881 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9470.

The product of its (nonzero) digits is 1024, while the sum is 28.

The square root of 21008881 is about 4583.5445890708. The cubic root of 21008881 is about 275.9313042292.

Adding to 21008881 its reverse (18880012), we get a palindrome (39888893).

The spelling of 21008881 in words is "twenty-one million, eight thousand, eight hundred eighty-one".