128505981 has 4 divisors (see below), whose sum is σ = 171341312. Its totient is φ = 85670652.

The previous prime is 128505977. The next prime is 128506019. The reversal of 128505981 is 189505821.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is not a de Polignac number, because 128505981 - 2² = 128505977 is a prime.

It is a super-2 number, since 2×128505981² = 33027574305544722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (128505901) 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, 21417661 + ... + 21417666.

It is an arithmetic number, because the mean of its divisors is an integer number (42835328).

Almost surely, 2^128505981 is an apocalyptic number.

It is an amenable number.

128505981 is a deficient number, since it is larger than the sum of its proper divisors (42835331).

128505981 is an equidigital number, since it uses as much as digits as its factorization.

128505981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 42835330.

The product of its (nonzero) digits is 28800, while the sum is 39.

The square root of 128505981 is about 11336.0478562857. The cubic root of 128505981 is about 504.6316053228.

The spelling of 128505981 in words is "one hundred twenty-eight million, five hundred five thousand, nine hundred eighty-one".