21791909 has 8 divisors (see below), whose sum is σ = 23146200. Its totient is φ = 20445696.

The previous prime is 21791897. The next prime is 21791911. The reversal of 21791909 is 90919712.

It can be written as a sum of positive squares in 4 ways, for example, as 3276100 + 18515809 = 1810^2 + 4303^2 .

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

It is not a de Polignac number, because 21791909 - 2²⁴ = 5014693 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21791969) 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, 4097 + ... + 7769.

It is an arithmetic number, because the mean of its divisors is an integer number (2893275).

Almost surely, 2^21791909 is an apocalyptic number.

It is an amenable number.

21791909 is a deficient number, since it is larger than the sum of its proper divisors (1354291).

21791909 is a wasteful number, since it uses less digits than its factorization.

21791909 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4039.

The product of its (nonzero) digits is 10206, while the sum is 38.

The square root of 21791909 is about 4668.1804806584. The cubic root of 21791909 is about 279.3176796188.

The spelling of 21791909 in words is "twenty-one million, seven hundred ninety-one thousand, nine hundred nine".