206721521 has 2 divisors, whose sum is σ = 206721522. Its totient is φ = 206721520.

The previous prime is 206721517. The next prime is 206721523. The reversal of 206721521 is 125127602.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 169937296 + 36784225 = 13036^2 + 6065^2 .

It is a cyclic number.

It is not a de Polignac number, because 206721521 - 2² = 206721517 is a prime.

Together with 206721523, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (206721523) 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, 103360760 + 103360761.

It is an arithmetic number, because the mean of its divisors is an integer number (103360761).

Almost surely, 2^206721521 is an apocalyptic number.

It is an amenable number.

206721521 is a deficient number, since it is larger than the sum of its proper divisors (1).

206721521 is an equidigital number, since it uses as much as digits as its factorization.

206721521 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1680, while the sum is 26.

The square root of 206721521 is about 14377.8134985818. The cubic root of 206721521 is about 591.2827791960.

The spelling of 206721521 in words is "two hundred six million, seven hundred twenty-one thousand, five hundred twenty-one".