991538 has 4 divisors (see below), whose sum is σ = 1487310. Its totient is φ = 495768.

The previous prime is 991531. The next prime is 991541. The reversal of 991538 is 835199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 835199 = 23 ⋅36313.

It can be written as a sum of positive squares in only one way, i.e., 877969 + 113569 = 937^2 + 337^2 .

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 991498 and 991507.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 991538.

It is not an unprimeable number, because it can be changed into a prime (991531) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 247883 + ... + 247886.

2⁹⁹¹⁵³⁸ is an apocalyptic number.

991538 is a deficient number, since it is larger than the sum of its proper divisors (495772).

991538 is a wasteful number, since it uses less digits than its factorization.

991538 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 495771.

The product of its digits is 9720, while the sum is 35.

The square root of 991538 is about 995.7600112477. The cubic root of 991538 is about 99.7171339558.

The spelling of 991538 in words is "nine hundred ninety-one thousand, five hundred thirty-eight".