687795721 has 2 divisors, whose sum is σ = 687795722. Its totient is φ = 687795720.

The previous prime is 687795677. The next prime is 687795727. The reversal of 687795721 is 127597786.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 626000400 + 61795321 = 25020^2 + 7861^2 .

It is a cyclic number.

It is not a de Polignac number, because 687795721 - 2⁷ = 687795593 is a prime.

It is not a weakly prime, because it can be changed into another prime (687795727) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343897860 + 343897861.

It is an arithmetic number, because the mean of its divisors is an integer number (343897861).

Almost surely, 2^687795721 is an apocalyptic number.

It is an amenable number.

687795721 is a deficient number, since it is larger than the sum of its proper divisors (1).

687795721 is an equidigital number, since it uses as much as digits as its factorization.

687795721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 1481760, while the sum is 52.

The square root of 687795721 is about 26225.8597761827. The cubic root of 687795721 is about 882.7136109209.

The spelling of 687795721 in words is "six hundred eighty-seven million, seven hundred ninety-five thousand, seven hundred twenty-one".