681872013721 has 4 divisors (see below), whose sum is σ = 681881872932. Its totient is φ = 681862154512.

The previous prime is 681872013677. The next prime is 681872013751. The reversal of 681872013721 is 127310278186.

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 404947686025 + 276924327696 = 636355^2 + 526236^2 .

It is a cyclic number.

It is not a de Polignac number, because 681872013721 - 2¹⁵ = 681871980953 is a prime.

It is a super-2 number, since 2×681872013721² (a number of 24 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (681872013751) 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, 4825126 + ... + 4964431.

It is an arithmetic number, because the mean of its divisors is an integer number (170470468233).

Almost surely, 2^681872013721 is an apocalyptic number.

It is an amenable number.

681872013721 is a deficient number, since it is larger than the sum of its proper divisors (9859211).

681872013721 is an equidigital number, since it uses as much as digits as its factorization.

681872013721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9859210.

The product of its (nonzero) digits is 225792, while the sum is 46.

The spelling of 681872013721 in words is "six hundred eighty-one billion, eight hundred seventy-two million, thirteen thousand, seven hundred twenty-one".