21390289 has 2 divisors, whose sum is σ = 21390290. Its totient is φ = 21390288.

The previous prime is 21390287. The next prime is 21390337. The reversal of 21390289 is 98209312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11730625 + 9659664 = 3425^2 + 3108^2 .

It is a cyclic number.

It is not a de Polignac number, because 21390289 - 2¹ = 21390287 is a prime.

Together with 21390287, it forms a pair of twin primes.

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, 10695144 + 10695145.

It is an arithmetic number, because the mean of its divisors is an integer number (10695145).

Almost surely, 2^21390289 is an apocalyptic number.

It is an amenable number.

21390289 is a deficient number, since it is larger than the sum of its proper divisors (1).

21390289 is an equidigital number, since it uses as much as digits as its factorization.

21390289 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 7776, while the sum is 34.

The square root of 21390289 is about 4624.9636755330. The cubic root of 21390289 is about 277.5911082494.

The spelling of 21390289 in words is "twenty-one million, three hundred ninety thousand, two hundred eighty-nine".