687506921 has 2 divisors, whose sum is σ = 687506922. Its totient is φ = 687506920.

The previous prime is 687506873. The next prime is 687506923. The reversal of 687506921 is 129605786.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 669774400 + 17732521 = 25880^2 + 4211^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-687506921 is a prime.

Together with 687506923, 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 (687506923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343753460 + 343753461.

It is an arithmetic number, because the mean of its divisors is an integer number (343753461).

Almost surely, 2^687506921 is an apocalyptic number.

It is an amenable number.

687506921 is a deficient number, since it is larger than the sum of its proper divisors (1).

687506921 is an equidigital number, since it uses as much as digits as its factorization.

687506921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 181440, while the sum is 44.

The square root of 687506921 is about 26220.3531822132. The cubic root of 687506921 is about 882.5900454629.

The spelling of 687506921 in words is "six hundred eighty-seven million, five hundred six thousand, nine hundred twenty-one".