687133721 has 4 divisors (see below), whose sum is σ = 688325172. Its totient is φ = 685942272.

The previous prime is 687133687. The next prime is 687133723. The reversal of 687133721 is 127331786.

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 366186496 + 320947225 = 19136^2 + 17915^2 .

It is a cyclic number.

It is not a de Polignac number, because 687133721 - 2¹⁰ = 687132697 is a prime.

It is a super-3 number, since 3×687133721³ (a number of 27 digits) contains 333 as substring.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (687133723) 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, 594860 + ... + 596013.

It is an arithmetic number, because the mean of its divisors is an integer number (172081293).

Almost surely, 2^687133721 is an apocalyptic number.

It is an amenable number.

687133721 is a deficient number, since it is larger than the sum of its proper divisors (1191451).

687133721 is a wasteful number, since it uses less digits than its factorization.

687133721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1191450.

The product of its digits is 42336, while the sum is 38.

The square root of 687133721 is about 26213.2356072271. The cubic root of 687133721 is about 882.4303175084.

The spelling of 687133721 in words is "six hundred eighty-seven million, one hundred thirty-three thousand, seven hundred twenty-one".