991689605 has 4 divisors (see below), whose sum is σ = 1190027532. Its totient is φ = 793351680.

The previous prime is 991689599. The next prime is 991689617. The reversal of 991689605 is 506986199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 506986199 = 20347 ⋅24917.

It can be written as a sum of positive squares in 2 ways, for example, as 200448964 + 791240641 = 14158^2 + 28129^2 .

It is not a de Polignac number, because 991689605 - 2¹⁶ = 991624069 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 99168956 + ... + 99168965.

It is an arithmetic number, because the mean of its divisors is an integer number (297506883).

Almost surely, 2^991689605 is an apocalyptic number.

It is an amenable number.

991689605 is a deficient number, since it is larger than the sum of its proper divisors (198337927).

991689605 is a wasteful number, since it uses less digits than its factorization.

991689605 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 198337926.

The product of its (nonzero) digits is 1049760, while the sum is 53.

The square root of 991689605 is about 31491.1035849809. The cubic root of 991689605 is about 997.2221590781. Note that the first 3 decimals are identical.

The spelling of 991689605 in words is "nine hundred ninety-one million, six hundred eighty-nine thousand, six hundred five".