210690721 has 2 divisors, whose sum is σ = 210690722. Its totient is φ = 210690720.

The previous prime is 210690719. The next prime is 210690743. The reversal of 210690721 is 127096012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 203205025 + 7485696 = 14255^2 + 2736^2 .

It is a cyclic number.

It is not a de Polignac number, because 210690721 - 2¹ = 210690719 is a prime.

Together with 210690719, it forms a pair of twin primes.

It is a self number, because there is not a number n which added to its sum of digits gives 210690721.

It is not a weakly prime, because it can be changed into another prime (210690761) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 105345360 + 105345361.

It is an arithmetic number, because the mean of its divisors is an integer number (105345361).

Almost surely, 2^210690721 is an apocalyptic number.

It is an amenable number.

210690721 is a deficient number, since it is larger than the sum of its proper divisors (1).

210690721 is an equidigital number, since it uses as much as digits as its factorization.

210690721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1512, while the sum is 28.

The square root of 210690721 is about 14515.1893201570. The cubic root of 210690721 is about 595.0431633118.

The spelling of 210690721 in words is "two hundred ten million, six hundred ninety thousand, seven hundred twenty-one".