687521 has 2 divisors, whose sum is σ = 687522. Its totient is φ = 687520.

The previous prime is 687517. The next prime is 687523. The reversal of 687521 is 125786.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 555025 + 132496 = 745^2 + 364^2 .

It is a cyclic number.

It is not a de Polignac number, because 687521 - 2² = 687517 is a prime.

It is a Sophie Germain prime.

Together with 687523, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (687523) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343760 + 343761.

It is an arithmetic number, because the mean of its divisors is an integer number (343761).

2⁶⁸⁷⁵²¹ is an apocalyptic number.

It is an amenable number.

687521 is a deficient number, since it is larger than the sum of its proper divisors (1).

687521 is an equidigital number, since it uses as much as digits as its factorization.

687521 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3360, while the sum is 29.

The square root of 687521 is about 829.1688609686. The cubic root of 687521 is about 88.2596070081.

The spelling of 687521 in words is "six hundred eighty-seven thousand, five hundred twenty-one".