128666821 has 4 divisors (see below), whose sum is σ = 129456352. Its totient is φ = 127877292.

The previous prime is 128666819. The next prime is 128666831.

128666821 is nontrivially palindromic in base 10.

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.

It is a cyclic number.

It is not a de Polignac number, because 128666821 - 2¹ = 128666819 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 (128666801) 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, 394521 + ... + 394846.

It is an arithmetic number, because the mean of its divisors is an integer number (32364088).

Almost surely, 2^128666821 is an apocalyptic number.

It is an amenable number.

128666821 is a deficient number, since it is larger than the sum of its proper divisors (789531).

128666821 is an equidigital number, since it uses as much as digits as its factorization.

128666821 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 789530.

The product of its digits is 55296, while the sum is 40.

The square root of 128666821 is about 11343.1398210548. The cubic root of 128666821 is about 504.8420523590.

The spelling of 128666821 in words is "one hundred twenty-eight million, six hundred sixty-six thousand, eight hundred twenty-one".