21381399 has 12 divisors (see below), whose sum is σ = 33260136. Its totient is φ = 13157712.

The previous prime is 21381389. The next prime is 21381407. The reversal of 21381399 is 99318312.

It is not a de Polignac number, because 21381399 - 2⁴ = 21381383 is a prime.

It is a hoax number, since the sum of its digits (36) coincides with the sum of the digits of its distinct prime factors.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21381379) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 91257 + ... + 91490.

It is an arithmetic number, because the mean of its divisors is an integer number (2771678).

Almost surely, 2^21381399 is an apocalyptic number.

21381399 is a deficient number, since it is larger than the sum of its proper divisors (11878737).

21381399 is a wasteful number, since it uses less digits than its factorization.

21381399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 182766 (or 182763 counting only the distinct ones).

The product of its digits is 11664, while the sum is 36.

The square root of 21381399 is about 4624.0024870236. The cubic root of 21381399 is about 277.5526464517.

The spelling of 21381399 in words is "twenty-one million, three hundred eighty-one thousand, three hundred ninety-nine".