21820287 has 4 divisors (see below), whose sum is σ = 29093720. Its totient is φ = 14546856.

The previous prime is 21820283. The next prime is 21820297. The reversal of 21820287 is 78202812.

It is a happy number.

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

It is not a de Polignac number, because 21820287 - 2² = 21820283 is a prime.

It is a super-2 number, since 2×21820287² = 952249849524738, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21820283) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3636712 + ... + 3636717.

It is an arithmetic number, because the mean of its divisors is an integer number (7273430).

Almost surely, 2^21820287 is an apocalyptic number.

21820287 is a deficient number, since it is larger than the sum of its proper divisors (7273433).

21820287 is an equidigital number, since it uses as much as digits as its factorization.

21820287 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 7273432.

The product of its (nonzero) digits is 3584, while the sum is 30.

The square root of 21820287 is about 4671.2190057843. The cubic root of 21820287 is about 279.4388719829.

The spelling of 21820287 in words is "twenty-one million, eight hundred twenty thousand, two hundred eighty-seven".