128761670021 has 4 divisors (see below), whose sum is σ = 128765431500. Its totient is φ = 128757908544.

The previous prime is 128761669999. The next prime is 128761670039. The reversal of 128761670021 is 120076167821.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 120076167821 = 37 ⋅3245301833.

It can be written as a sum of positive squares in 2 ways, for example, as 110762496100 + 17999173921 = 332810^2 + 134161^2 .

It is a cyclic number.

It is not a de Polignac number, because 128761670021 - 2¹⁸ = 128761407877 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128761670041) 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, 1828916 + ... + 1898013.

It is an arithmetic number, because the mean of its divisors is an integer number (32191357875).

Almost surely, 2^128761670021 is an apocalyptic number.

It is an amenable number.

128761670021 is a deficient number, since it is larger than the sum of its proper divisors (3761479).

128761670021 is an equidigital number, since it uses as much as digits as its factorization.

128761670021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3761478.

The product of its (nonzero) digits is 56448, while the sum is 41.

The spelling of 128761670021 in words is "one hundred twenty-eight billion, seven hundred sixty-one million, six hundred seventy thousand, twenty-one".