21390287 has 2 divisors, whose sum is σ = 21390288. Its totient is φ = 21390286.

The previous prime is 21390283. The next prime is 21390289. The reversal of 21390287 is 78209312.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 21390287 - 2² = 21390283 is a prime.

Together with 21390289, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21390283) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10695143 + 10695144.

It is an arithmetic number, because the mean of its divisors is an integer number (10695144).

Almost surely, 2^21390287 is an apocalyptic number.

21390287 is a deficient number, since it is larger than the sum of its proper divisors (1).

21390287 is an equidigital number, since it uses as much as digits as its factorization.

21390287 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6048, while the sum is 32.

The square root of 21390287 is about 4624.9634593151. The cubic root of 21390287 is about 277.5910995978.

Adding to 21390287 its reverse (78209312), we get a palindrome (99599599).

The spelling of 21390287 in words is "twenty-one million, three hundred ninety thousand, two hundred eighty-seven".