21697109 has 4 divisors (see below), whose sum is σ = 24796704. Its totient is φ = 18597516.

The previous prime is 21697099. The next prime is 21697111. The reversal of 21697109 is 90179612.

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 not a de Polignac number, because 21697109 - 2¹² = 21693013 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 (21697129) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1549787 + ... + 1549800.

It is an arithmetic number, because the mean of its divisors is an integer number (6199176).

Almost surely, 2^21697109 is an apocalyptic number.

It is an amenable number.

21697109 is a deficient number, since it is larger than the sum of its proper divisors (3099595).

21697109 is an equidigital number, since it uses as much as digits as its factorization.

21697109 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3099594.

The product of its (nonzero) digits is 6804, while the sum is 35.

The square root of 21697109 is about 4658.0155645940. The cubic root of 21697109 is about 278.9120580307.

The spelling of 21697109 in words is "twenty-one million, six hundred ninety-seven thousand, one hundred nine".