991813841 has 4 divisors (see below), whose sum is σ = 991877232. Its totient is φ = 991750452.

The previous prime is 991813819. The next prime is 991813853. The reversal of 991813841 is 148318199.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also a brilliant number, because the two primes have the same length, and also an emirpimes, since its reverse is a distinct semiprime: 148318199 = 19 ⋅7806221.

It is a cyclic number.

It is not a de Polignac number, because 991813841 - 2¹⁸ = 991551697 is a prime.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 991813792 and 991813801.

It is not an unprimeable number, because it can be changed into a prime (991813871) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 10490 + ... + 45756.

It is an arithmetic number, because the mean of its divisors is an integer number (247969308).

Almost surely, 2^991813841 is an apocalyptic number.

It is an amenable number.

991813841 is a deficient number, since it is larger than the sum of its proper divisors (63391).

991813841 is a wasteful number, since it uses less digits than its factorization.

991813841 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 63390.

The product of its digits is 62208, while the sum is 44.

The square root of 991813841 is about 31493.0760803069. The cubic root of 991813841 is about 997.2638003734.

The spelling of 991813841 in words is "nine hundred ninety-one million, eight hundred thirteen thousand, eight hundred forty-one".