1687616721 has 16 divisors (see below), whose sum is σ = 2857340800. Its totient is φ = 964352304.

The previous prime is 1687616717. The next prime is 1687616729. The reversal of 1687616721 is 1276167861.

1687616721 is a `hidden beast` number, since 1 + 6 + 8 + 7 + 616 + 7 + 21 = 666.

It is not a de Polignac number, because 1687616721 - 2² = 1687616717 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1687616729) 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 in 15 ways as a sum of consecutive naturals, for example, 4464406 + ... + 4464783.

It is an arithmetic number, because the mean of its divisors is an integer number (178583800).

Almost surely, 2^1687616721 is an apocalyptic number.

It is an amenable number.

1687616721 is a deficient number, since it is larger than the sum of its proper divisors (1169724079).

1687616721 is an equidigital number, since it uses as much as digits as its factorization.

1687616721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8929205 (or 8929199 counting only the distinct ones).

The product of its digits is 169344, while the sum is 45.

The square root of 1687616721 is about 41080.6124710915. The cubic root of 1687616721 is about 1190.5782376823.

The spelling of 1687616721 in words is "one billion, six hundred eighty-seven million, six hundred sixteen thousand, seven hundred twenty-one".