21694399 has 4 divisors (see below), whose sum is σ = 22018264. Its totient is φ = 21370536.

The previous prime is 21694391. The next prime is 21694423. The reversal of 21694399 is 99349612.

21694399 = T₇₇₁ + T₇₇₂ + ... + T₈₃₇.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21694399 - 2³ = 21694391 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 (21694391) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 161832 + ... + 161965.

It is an arithmetic number, because the mean of its divisors is an integer number (5504566).

Almost surely, 2^21694399 is an apocalyptic number.

21694399 is a deficient number, since it is larger than the sum of its proper divisors (323865).

21694399 is an equidigital number, since it uses as much as digits as its factorization.

21694399 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 323864.

The product of its digits is 104976, while the sum is 43.

The square root of 21694399 is about 4657.7246591013. The cubic root of 21694399 is about 278.9004453753.

The spelling of 21694399 in words is "twenty-one million, six hundred ninety-four thousand, three hundred ninety-nine".