128812721 has 2 divisors, whose sum is σ = 128812722. Its totient is φ = 128812720.

The previous prime is 128812709. The next prime is 128812741. The reversal of 128812721 is 127218821.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 101103025 + 27709696 = 10055^2 + 5264^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-128812721 is a prime.

It is equal to p_7314638 and since 128812721 and 7314638 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 (128812741) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64406360 + 64406361.

It is an arithmetic number, because the mean of its divisors is an integer number (64406361).

Almost surely, 2^128812721 is an apocalyptic number.

It is an amenable number.

128812721 is a deficient number, since it is larger than the sum of its proper divisors (1).

128812721 is an equidigital number, since it uses as much as digits as its factorization.

128812721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3584, while the sum is 32.

The square root of 128812721 is about 11349.5691988727. The cubic root of 128812721 is about 505.0327998825.

The spelling of 128812721 in words is "one hundred twenty-eight million, eight hundred twelve thousand, seven hundred twenty-one".