128731681 has 4 divisors (see below), whose sum is σ = 138634132. Its totient is φ = 118829232.

The previous prime is 128731661. The next prime is 128731693. The reversal of 128731681 is 186137821.

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 33005025 + 95726656 = 5745^2 + 9784^2 .

It is a cyclic number.

It is not a de Polignac number, because 128731681 - 2⁷ = 128731553 is a prime.

It is a super-2 number, since 2×128731681² = 33143691386171522, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 128731681.

It is not an unprimeable number, because it can be changed into a prime (128731661) 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, 4951206 + ... + 4951231.

It is an arithmetic number, because the mean of its divisors is an integer number (34658533).

Almost surely, 2^128731681 is an apocalyptic number.

It is an amenable number.

128731681 is a deficient number, since it is larger than the sum of its proper divisors (9902451).

128731681 is an equidigital number, since it uses as much as digits as its factorization.

128731681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9902450.

The product of its digits is 16128, while the sum is 37.

The square root of 128731681 is about 11345.9984576061. The cubic root of 128731681 is about 504.9268671667.

The spelling of 128731681 in words is "one hundred twenty-eight million, seven hundred thirty-one thousand, six hundred eighty-one".