216021391 has 2 divisors, whose sum is σ = 216021392. Its totient is φ = 216021390.

The previous prime is 216021389. The next prime is 216021413. The reversal of 216021391 is 193120612.

216021391 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 216021391 - 2¹ = 216021389 is a prime.

Together with 216021389, it forms a pair of twin primes.

It is a zygodrome in base 2.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (216021301) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108010695 + 108010696.

It is an arithmetic number, because the mean of its divisors is an integer number (108010696).

Almost surely, 2^216021391 is an apocalyptic number.

216021391 is a deficient number, since it is larger than the sum of its proper divisors (1).

216021391 is an equidigital number, since it uses as much as digits as its factorization.

216021391 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 648, while the sum is 25.

The square root of 216021391 is about 14697.6661752810. Note that the first 3 decimals coincide. The cubic root of 216021391 is about 600.0198058277.

The spelling of 216021391 in words is "two hundred sixteen million, twenty-one thousand, three hundred ninety-one".