21808287 has 12 divisors (see below), whose sum is σ = 31557240. Its totient is φ = 14512848.

The previous prime is 21808271. The next prime is 21808291. The reversal of 21808287 is 78280812.

It is not a de Polignac number, because 21808287 - 2⁴ = 21808271 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21808217) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 4093 + ... + 7769.

It is an arithmetic number, because the mean of its divisors is an integer number (2629770).

Almost surely, 2^21808287 is an apocalyptic number.

21808287 is a deficient number, since it is larger than the sum of its proper divisors (9748953).

21808287 is a wasteful number, since it uses less digits than its factorization.

21808287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4342 (or 4339 counting only the distinct ones).

The product of its (nonzero) digits is 14336, while the sum is 36.

The square root of 21808287 is about 4669.9343678472. The cubic root of 21808287 is about 279.3876370723.

The spelling of 21808287 in words is "twenty-one million, eight hundred eight thousand, two hundred eighty-seven".