128211991 has 2 divisors, whose sum is σ = 128211992. Its totient is φ = 128211990.

The previous prime is 128211949. The next prime is 128212033. The reversal of 128211991 is 199112821.

It is a balanced prime because it is at equal distance from previous prime (128211949) and next prime (128212033).

It is a cyclic number.

It is not a de Polignac number, because 128211991 - 2²⁵ = 94657559 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (128211901) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64105995 + 64105996.

It is an arithmetic number, because the mean of its divisors is an integer number (64105996).

Almost surely, 2^128211991 is an apocalyptic number.

128211991 is a deficient number, since it is larger than the sum of its proper divisors (1).

128211991 is an equidigital number, since it uses as much as digits as its factorization.

128211991 is an evil number, because the sum of its binary digits is even.

The product of its digits is 2592, while the sum is 34.

The square root of 128211991 is about 11323.0733902064. The cubic root of 128211991 is about 504.2464872580.

The spelling of 128211991 in words is "one hundred twenty-eight million, two hundred eleven thousand, nine hundred ninety-one".