687721537 has 4 divisors (see below), whose sum is σ = 691696980. Its totient is φ = 683746096.

The previous prime is 687721499. The next prime is 687721547. The reversal of 687721537 is 735127786.

687721537 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 304188481 + 383533056 = 17441^2 + 19584^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-687721537 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (687721547) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1987462 + ... + 1987807.

It is an arithmetic number, because the mean of its divisors is an integer number (172924245).

Almost surely, 2^687721537 is an apocalyptic number.

It is an amenable number.

687721537 is a deficient number, since it is larger than the sum of its proper divisors (3975443).

687721537 is a wasteful number, since it uses less digits than its factorization.

687721537 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3975442.

The product of its digits is 493920, while the sum is 46.

The square root of 687721537 is about 26224.4454088166. The cubic root of 687721537 is about 882.6818739875.

The spelling of 687721537 in words is "six hundred eighty-seven million, seven hundred twenty-one thousand, five hundred thirty-seven".