128917561 has 4 divisors (see below), whose sum is σ = 133076224. Its totient is φ = 124758900.

The previous prime is 128917543. The next prime is 128917577. The reversal of 128917561 is 165719821.

It is a happy number.

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 a cyclic number.

It is not a de Polignac number, because 128917561 - 2⁹ = 128917049 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128917531) 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, 2079285 + ... + 2079346.

It is an arithmetic number, because the mean of its divisors is an integer number (33269056).

Almost surely, 2^128917561 is an apocalyptic number.

It is an amenable number.

128917561 is a deficient number, since it is larger than the sum of its proper divisors (4158663).

128917561 is an equidigital number, since it uses as much as digits as its factorization.

128917561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 4158662.

The product of its digits is 30240, while the sum is 40.

The square root of 128917561 is about 11354.1869369850. The cubic root of 128917561 is about 505.1697772457.

The spelling of 128917561 in words is "one hundred twenty-eight million, nine hundred seventeen thousand, five hundred sixty-one".