216821807 has 2 divisors, whose sum is σ = 216821808. Its totient is φ = 216821806.

The previous prime is 216821789. The next prime is 216821809. The reversal of 216821807 is 708128612.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 216821807 - 2⁶ = 216821743 is a prime.

Together with 216821809, 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 (216821809) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 108410903 + 108410904.

It is an arithmetic number, because the mean of its divisors is an integer number (108410904).

Almost surely, 2^216821807 is an apocalyptic number.

216821807 is a deficient number, since it is larger than the sum of its proper divisors (1).

216821807 is an equidigital number, since it uses as much as digits as its factorization.

216821807 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 10752, while the sum is 35.

The square root of 216821807 is about 14724.8703559658. The cubic root of 216821807 is about 600.7599694118.

The spelling of 216821807 in words is "two hundred sixteen million, eight hundred twenty-one thousand, eight hundred seven".