21891709 has 4 divisors (see below), whose sum is σ = 25019104. Its totient is φ = 18764316.

The previous prime is 21891691. The next prime is 21891719. The reversal of 21891709 is 90719812.

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 21891709 - 2⁵ = 21891677 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 (21891719) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1563687 + ... + 1563700.

It is an arithmetic number, because the mean of its divisors is an integer number (6254776).

Almost surely, 2^21891709 is an apocalyptic number.

It is an amenable number.

21891709 is a deficient number, since it is larger than the sum of its proper divisors (3127395).

21891709 is an equidigital number, since it uses as much as digits as its factorization.

21891709 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3127394.

The product of its (nonzero) digits is 9072, while the sum is 37.

The square root of 21891709 is about 4678.8576597285. The cubic root of 21891709 is about 279.7434256776.

The spelling of 21891709 in words is "twenty-one million, eight hundred ninety-one thousand, seven hundred nine".