21000399 has 16 divisors (see below), whose sum is σ = 32683008. Its totient is φ = 11744352.

The previous prime is 21000391. The next prime is 21000407. The reversal of 21000399 is 99300012.

It is a happy number.

It is an interprime number because it is at equal distance from previous prime (21000391) and next prime (21000407).

It is not a de Polignac number, because 21000399 - 2³ = 21000391 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21000391) 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 15 ways as a sum of consecutive naturals, for example, 9652 + ... + 11625.

It is an arithmetic number, because the mean of its divisors is an integer number (2042688).

Almost surely, 2^21000399 is an apocalyptic number.

21000399 is a deficient number, since it is larger than the sum of its proper divisors (11682609).

21000399 is a wasteful number, since it uses less digits than its factorization.

21000399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 21334.

The product of its (nonzero) digits is 486, while the sum is 24.

The square root of 21000399 is about 4582.6192292182. The cubic root of 21000399 is about 275.8941649457.

The spelling of 21000399 in words is "twenty-one million, three hundred ninety-nine", and thus it is an aban number.