21706399 has 16 divisors (see below), whose sum is σ = 27004320. Its totient is φ = 17141760.

The previous prime is 21706387. The next prime is 21706427. The reversal of 21706399 is 99360712.

It is a cyclic number.

It is not a de Polignac number, because 21706399 - 2¹¹ = 21704351 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 (21706199) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 2034 + ... + 6895.

It is an arithmetic number, because the mean of its divisors is an integer number (1687770).

Almost surely, 2^21706399 is an apocalyptic number.

21706399 is a deficient number, since it is larger than the sum of its proper divisors (5297921).

21706399 is a wasteful number, since it uses less digits than its factorization.

21706399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8970.

The product of its (nonzero) digits is 20412, while the sum is 37.

The square root of 21706399 is about 4659.0126636445. The cubic root of 21706399 is about 278.9518593901.

The spelling of 21706399 in words is "twenty-one million, seven hundred six thousand, three hundred ninety-nine".