21616399 has 12 divisors (see below), whose sum is σ = 25827384. Its totient is φ = 18026064.

The previous prime is 21616373. The next prime is 21616417. The reversal of 21616399 is 99361612.

It is not a de Polignac number, because 21616399 - 2¹⁷ = 21485327 is a prime.

It is a Harshad number since it is a multiple of its sum of digits (37).

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21616349) 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, 4149 + ... + 7774.

It is an arithmetic number, because the mean of its divisors is an integer number (2152282).

Almost surely, 2^21616399 is an apocalyptic number.

21616399 is a deficient number, since it is larger than the sum of its proper divisors (4210985).

21616399 is a wasteful number, since it uses less digits than its factorization.

21616399 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11974 (or 11967 counting only the distinct ones).

The product of its digits is 17496, while the sum is 37.

The square root of 21616399 is about 4649.3439322124. The cubic root of 21616399 is about 278.5657912763.

The spelling of 21616399 in words is "twenty-one million, six hundred sixteen thousand, three hundred ninety-nine".