128500721 has 2 divisors, whose sum is σ = 128500722. Its totient is φ = 128500720.

The previous prime is 128500703. The next prime is 128500733. The reversal of 128500721 is 127005821.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 128482225 + 18496 = 11335^2 + 136^2 .

It is an emirp because it is prime and its reverse (127005821) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 128500721 - 2¹⁰ = 128499697 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (128500621) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 64250360 + 64250361.

It is an arithmetic number, because the mean of its divisors is an integer number (64250361).

Almost surely, 2^128500721 is an apocalyptic number.

It is an amenable number.

128500721 is a deficient number, since it is larger than the sum of its proper divisors (1).

128500721 is an equidigital number, since it uses as much as digits as its factorization.

128500721 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1120, while the sum is 26.

The square root of 128500721 is about 11335.8158506567. The cubic root of 128500721 is about 504.6247200441.

The spelling of 128500721 in words is "one hundred twenty-eight million, five hundred thousand, seven hundred twenty-one".