21404287 has 4 divisors (see below), whose sum is σ = 21413560. Its totient is φ = 21395016.

The previous prime is 21404269. The next prime is 21404303. The reversal of 21404287 is 78240412.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It is a cyclic number.

It is not a de Polignac number, because 21404287 - 2¹¹ = 21402239 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 (21404267) 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, 1873 + ... + 6805.

It is an arithmetic number, because the mean of its divisors is an integer number (5353390).

Almost surely, 2^21404287 is an apocalyptic number.

21404287 is a deficient number, since it is larger than the sum of its proper divisors (9273).

21404287 is an equidigital number, since it uses as much as digits as its factorization.

21404287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9272.

The product of its (nonzero) digits is 3584, while the sum is 28.

The square root of 21404287 is about 4626.4767372159. The cubic root of 21404287 is about 277.6516477622.

Adding to 21404287 its reverse (78240412), we get a palindrome (99644699).

The spelling of 21404287 in words is "twenty-one million, four hundred four thousand, two hundred eighty-seven".