21109997 has 4 divisors (see below), whose sum is σ = 21119196. Its totient is φ = 21100800.

The previous prime is 21109987. The next prime is 21110027. The reversal of 21109997 is 79990112.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 11162281 + 9947716 = 3341^2 + 3154^2 .

It is a cyclic number.

It is not a de Polignac number, because 21109997 - 2¹⁴ = 21093613 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21109997.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21109927) 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, 1997 + ... + 6797.

It is an arithmetic number, because the mean of its divisors is an integer number (5279799).

Almost surely, 2^21109997 is an apocalyptic number.

It is an amenable number.

21109997 is a deficient number, since it is larger than the sum of its proper divisors (9199).

21109997 is an equidigital number, since it uses as much as digits as its factorization.

21109997 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9198.

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

The square root of 21109997 is about 4594.5616765911. The cubic root of 21109997 is about 276.3732828118.

The spelling of 21109997 in words is "twenty-one million, one hundred nine thousand, nine hundred ninety-seven".