21606399 has 8 divisors (see below), whose sum is σ = 32009520. Its totient is φ = 14404248.

The previous prime is 21606359. The next prime is 21606419. The reversal of 21606399 is 99360612.

21606399 is a `hidden beast` number, since 2 + 16 + 0 + 639 + 9 = 666.

It is not a de Polignac number, because 21606399 - 2⁷ = 21606271 is a prime.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21606359) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 400092 + ... + 400145.

It is an arithmetic number, because the mean of its divisors is an integer number (4001190).

Almost surely, 2^21606399 is an apocalyptic number.

21606399 is a deficient number, since it is larger than the sum of its proper divisors (10403121).

21606399 is an equidigital number, since it uses as much as digits as its factorization.

21606399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 800246 (or 800240 counting only the distinct ones).

The product of its (nonzero) digits is 17496, while the sum is 36.

The square root of 21606399 is about 4648.2683872599. The cubic root of 21606399 is about 278.5228287153.

The spelling of 21606399 in words is "twenty-one million, six hundred six thousand, three hundred ninety-nine".