128391561 has 15 divisors (see below), whose sum is σ = 191947261. Its totient is φ = 85526388.

The previous prime is 128391533. The next prime is 128391619. The reversal of 128391561 is 165193821.

The square root of 128391561 is 11331.

It is a perfect power (a square), and thus also a powerful number.

128391561 is a `hidden beast` number, since 1 + 2 + 8 + 3 + 91 + 561 = 666.

It is not a de Polignac number, because 128391561 - 2¹⁹ = 127867273 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (128391521) by changing a digit.

It is a polite number, since it can be written in 14 ways as a sum of consecutive naturals, for example, 101350 + ... + 102608.

Almost surely, 2^128391561 is an apocalyptic number.

128391561 is the 11331-st square number.

128391561 is the 5666-th centered octagonal number.

It is an amenable number.

128391561 is a deficient number, since it is larger than the sum of its proper divisors (63555700).

128391561 is an frugal number, since it uses more digits than its factorization.

128391561 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2530 (or 1262 counting only the distinct ones).

The product of its digits is 12960, while the sum is 36.

The cubic root of 128391561 is about 504.4817884471.

Multiplying 128391561 by its sum of digits (36), we get a square (4622096196 = 67986²).

It can be divided in two parts, 12839 and 1561, that added together give a square (14400 = 120²).

The spelling of 128391561 in words is "one hundred twenty-eight million, three hundred ninety-one thousand, five hundred sixty-one".