991790135906 has 4 divisors (see below), whose sum is σ = 1487685203862. Its totient is φ = 495895067952.

The previous prime is 991790135899. The next prime is 991790135909. The reversal of 991790135906 is 609531097199.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in only one way, i.e., 834407344681 + 157382791225 = 913459^2 + 396715^2 .

It is not an unprimeable number, because it can be changed into a prime (991790135909) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 247947533975 + ... + 247947533978.

Almost surely, 2^991790135906 is an apocalyptic number.

991790135906 is a deficient number, since it is larger than the sum of its proper divisors (495895067956).

991790135906 is a wasteful number, since it uses less digits than its factorization.

991790135906 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 495895067955.

The product of its (nonzero) digits is 4133430, while the sum is 59.

The spelling of 991790135906 in words is "nine hundred ninety-one billion, seven hundred ninety million, one hundred thirty-five thousand, nine hundred six".