687455721 has 16 divisors (see below), whose sum is σ = 1051307520. Its totient is φ = 443519280.

The previous prime is 687455693. The next prime is 687455723. The reversal of 687455721 is 127554786.

687455721 is a `hidden beast` number, since 6 + 8 + 74 + 5 + 572 + 1 = 666.

It is not a de Polignac number, because 687455721 - 2¹⁹ = 686931433 is a prime.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (687455723) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 409830 + ... + 411503.

It is an arithmetic number, because the mean of its divisors is an integer number (65706720).

Almost surely, 2^687455721 is an apocalyptic number.

It is an amenable number.

687455721 is a deficient number, since it is larger than the sum of its proper divisors (363851799).

687455721 is a wasteful number, since it uses less digits than its factorization.

687455721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 821373 (or 821367 counting only the distinct ones).

The product of its digits is 470400, while the sum is 45.

The square root of 687455721 is about 26219.3768232580. The cubic root of 687455721 is about 882.5681355103.

The spelling of 687455721 in words is "six hundred eighty-seven million, four hundred fifty-five thousand, seven hundred twenty-one".