128158721 has 2 divisors, whose sum is σ = 128158722. Its totient is φ = 128158720.

The previous prime is 128158703. The next prime is 128158729. The reversal of 128158721 is 127851821.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 90459121 + 37699600 = 9511^2 + 6140^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-128158721 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is equal to p_7279541 and since 128158721 and 7279541 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (128158729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64079360 + 64079361.

It is an arithmetic number, because the mean of its divisors is an integer number (64079361).

Almost surely, 2^128158721 is an apocalyptic number.

It is an amenable number.

128158721 is a deficient number, since it is larger than the sum of its proper divisors (1).

128158721 is an equidigital number, since it uses as much as digits as its factorization.

128158721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 8960, while the sum is 35.

The square root of 128158721 is about 11320.7208692733. The cubic root of 128158721 is about 504.1766421753.

The spelling of 128158721 in words is "one hundred twenty-eight million, one hundred fifty-eight thousand, seven hundred twenty-one".