21100921 has 4 divisors (see below), whose sum is σ = 21338100. Its totient is φ = 20863744.

The previous prime is 21100909. The next prime is 21100931. The reversal of 21100921 is 12900112.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 1784896 + 19316025 = 1336^2 + 4395^2 .

It is a cyclic number.

It is not a de Polignac number, because 21100921 - 2²³ = 12712313 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21100895 and 21100904.

It is not an unprimeable number, because it can be changed into a prime (21100901) 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, 118456 + ... + 118633.

It is an arithmetic number, because the mean of its divisors is an integer number (5334525).

Almost surely, 2^21100921 is an apocalyptic number.

It is an amenable number.

21100921 is a deficient number, since it is larger than the sum of its proper divisors (237179).

21100921 is an equidigital number, since it uses as much as digits as its factorization.

21100921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 237178.

The product of its (nonzero) digits is 36, while the sum is 16.

The square root of 21100921 is about 4593.5738809776. The cubic root of 21100921 is about 276.3336692979. Note that the first 3 decimals are identical.

The spelling of 21100921 in words is "twenty-one million, one hundred thousand, nine hundred twenty-one".