128235905661 has 4 divisors (see below), whose sum is σ = 170981207552. Its totient is φ = 85490603772.

The previous prime is 128235905587. The next prime is 128235905683. The reversal of 128235905661 is 166509532821.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 166509532821 = 3 ⋅55503177607.

It is not a de Polignac number, because 128235905661 - 2¹⁴ = 128235889277 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 128235905661.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128235905261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 21372650941 + ... + 21372650946.

It is an arithmetic number, because the mean of its divisors is an integer number (42745301888).

Almost surely, 2^128235905661 is an apocalyptic number.

It is an amenable number.

128235905661 is a deficient number, since it is larger than the sum of its proper divisors (42745301891).

128235905661 is an equidigital number, since it uses as much as digits as its factorization.

128235905661 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 42745301890.

The product of its (nonzero) digits is 777600, while the sum is 48.

The spelling of 128235905661 in words is "one hundred twenty-eight billion, two hundred thirty-five million, nine hundred five thousand, six hundred sixty-one".