687649381 has 2 divisors, whose sum is σ = 687649382. Its totient is φ = 687649380.

The previous prime is 687649379. The next prime is 687649427. The reversal of 687649381 is 183946786.

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., 473758756 + 213890625 = 21766^2 + 14625^2 .

It is a cyclic number.

It is not a de Polignac number, because 687649381 - 2¹ = 687649379 is a prime.

It is a super-2 number, since 2×687649381² = 945723342379366322, which contains 22 as substring.

Together with 687649379, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (687649351) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343824690 + 343824691.

It is an arithmetic number, because the mean of its divisors is an integer number (343824691).

Almost surely, 2^687649381 is an apocalyptic number.

It is an amenable number.

687649381 is a deficient number, since it is larger than the sum of its proper divisors (1).

687649381 is an equidigital number, since it uses as much as digits as its factorization.

687649381 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1741824, while the sum is 52.

The square root of 687649381 is about 26223.0696334354. The cubic root of 687649381 is about 882.6510024707.

The spelling of 687649381 in words is "six hundred eighty-seven million, six hundred forty-nine thousand, three hundred eighty-one".