21689399 has 4 divisors (see below), whose sum is σ = 22965264. Its totient is φ = 20413536.

The previous prime is 21689383. The next prime is 21689407. The reversal of 21689399 is 99398612.

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 21689399 - 2⁴ = 21689383 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 (21689309) 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, 637907 + ... + 637940.

It is an arithmetic number, because the mean of its divisors is an integer number (5741316).

Almost surely, 2^21689399 is an apocalyptic number.

21689399 is a deficient number, since it is larger than the sum of its proper divisors (1275865).

21689399 is a wasteful number, since it uses less digits than its factorization.

21689399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1275864.

The product of its digits is 209952, while the sum is 47.

The square root of 21689399 is about 4657.1878854090. The cubic root of 21689399 is about 278.8790172735.

The spelling of 21689399 in words is "twenty-one million, six hundred eighty-nine thousand, three hundred ninety-nine".