681710921 has 4 divisors (see below), whose sum is σ = 682349700. Its totient is φ = 681072144.

The previous prime is 681710873. The next prime is 681710923. The reversal of 681710921 is 129017186.

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 541027600 + 140683321 = 23260^2 + 11861^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-681710921 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (681710923) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 317786 + ... + 319923.

It is an arithmetic number, because the mean of its divisors is an integer number (170587425).

Almost surely, 2^681710921 is an apocalyptic number.

It is an amenable number.

681710921 is a deficient number, since it is larger than the sum of its proper divisors (638779).

681710921 is a wasteful number, since it uses less digits than its factorization.

681710921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 638778.

The product of its (nonzero) digits is 6048, while the sum is 35.

The square root of 681710921 is about 26109.5944242725. The cubic root of 681710921 is about 880.1028293233.

The spelling of 681710921 in words is "six hundred eighty-one million, seven hundred ten thousand, nine hundred twenty-one".