83128721 has 4 divisors (see below), whose sum is σ = 89523252. Its totient is φ = 76734192.

The previous prime is 83128711. The next prime is 83128729. The reversal of 83128721 is 12782138.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12782138 = 2 ⋅6391069.

It can be written as a sum of positive squares in 2 ways, for example, as 28944400 + 54184321 = 5380^2 + 7361^2 .

It is a cyclic number.

It is not a de Polignac number, because 83128721 - 2¹⁰ = 83127697 is a prime.

It is not an unprimeable number, because it can be changed into a prime (83128729) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 3197246 + ... + 3197271.

It is an arithmetic number, because the mean of its divisors is an integer number (22380813).

Almost surely, 2^83128721 is an apocalyptic number.

It is an amenable number.

83128721 is a deficient number, since it is larger than the sum of its proper divisors (6394531).

83128721 is a wasteful number, since it uses less digits than its factorization.

83128721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6394530.

The product of its digits is 5376, while the sum is 32.

The square root of 83128721 is about 9117.4953249234. The cubic root of 83128721 is about 436.4324487059.

The spelling of 83128721 in words is "eighty-three million, one hundred twenty-eight thousand, seven hundred twenty-one".