128666921 has 2 divisors, whose sum is σ = 128666922. Its totient is φ = 128666920.

The previous prime is 128666893. The next prime is 128666929. The reversal of 128666921 is 129666821.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 84842521 + 43824400 = 9211^2 + 6620^2 .

It is a cyclic number.

It is not a de Polignac number, because 128666921 - 2¹⁸ = 128404777 is a prime.

It is not a weakly prime, because it can be changed into another prime (128666929) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64333460 + 64333461.

It is an arithmetic number, because the mean of its divisors is an integer number (64333461).

Almost surely, 2^128666921 is an apocalyptic number.

It is an amenable number.

128666921 is a deficient number, since it is larger than the sum of its proper divisors (1).

128666921 is an equidigital number, since it uses as much as digits as its factorization.

128666921 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 62208, while the sum is 41.

The square root of 128666921 is about 11343.1442290046. The cubic root of 128666921 is about 504.8421831469.

The spelling of 128666921 in words is "one hundred twenty-eight million, six hundred sixty-six thousand, nine hundred twenty-one".