128991587 has 4 divisors (see below), whose sum is σ = 129192840. Its totient is φ = 128790336.

The previous prime is 128991557. The next prime is 128991607. The reversal of 128991587 is 785199821.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 128991587 - 2¹⁸ = 128729443 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128991557) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 99662 + ... + 100947.

It is an arithmetic number, because the mean of its divisors is an integer number (32298210).

Almost surely, 2^128991587 is an apocalyptic number.

128991587 is a deficient number, since it is larger than the sum of its proper divisors (201253).

128991587 is an equidigital number, since it uses as much as digits as its factorization.

128991587 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 201252.

The product of its digits is 362880, while the sum is 50.

The square root of 128991587 is about 11357.4463238881. The cubic root of 128991587 is about 505.2664502468.

The spelling of 128991587 in words is "one hundred twenty-eight million, nine hundred ninety-one thousand, five hundred eighty-seven".