128779991 has 2 divisors, whose sum is σ = 128779992. Its totient is φ = 128779990.

The previous prime is 128779961. The next prime is 128780011. The reversal of 128779991 is 199977821.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 128779991 - 2⁶ = 128779927 is a prime.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (128779901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64389995 + 64389996.

It is an arithmetic number, because the mean of its divisors is an integer number (64389996).

Almost surely, 2^128779991 is an apocalyptic number.

128779991 is a deficient number, since it is larger than the sum of its proper divisors (1).

128779991 is an equidigital number, since it uses as much as digits as its factorization.

128779991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 571536, while the sum is 53.

The square root of 128779991 is about 11348.1272023185. The cubic root of 128779991 is about 504.9900216961.

The spelling of 128779991 in words is "one hundred twenty-eight million, seven hundred seventy-nine thousand, nine hundred ninety-one".