21697999 has 4 divisors (see below), whose sum is σ = 21725064. Its totient is φ = 21670936.

The previous prime is 21697997. The next prime is 21698029. The reversal of 21697999 is 99979612.

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

It is a cyclic number.

It is not a de Polignac number, because 21697999 - 2¹ = 21697997 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 (21697997) 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, 12292 + ... + 13945.

It is an arithmetic number, because the mean of its divisors is an integer number (5431266).

Almost surely, 2^21697999 is an apocalyptic number.

21697999 is a deficient number, since it is larger than the sum of its proper divisors (27065).

21697999 is an equidigital number, since it uses as much as digits as its factorization.

21697999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 27064.

The product of its digits is 551124, while the sum is 52.

The square root of 21697999 is about 4658.1110978593. Note that the first 3 decimals coincide. The cubic root of 21697999 is about 278.9158715700.

The spelling of 21697999 in words is "twenty-one million, six hundred ninety-seven thousand, nine hundred ninety-nine".