991897897 has 4 divisors (see below), whose sum is σ = 998215876. Its totient is φ = 985579920.

The previous prime is 991897889. The next prime is 991897901. The reversal of 991897897 is 798798199.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 798798199 = 6833 ⋅116903.

It can be written as a sum of positive squares in 2 ways, for example, as 356303376 + 635594521 = 18876^2 + 25211^2 .

It is a cyclic number.

It is not a de Polignac number, because 991897897 - 2³ = 991897889 is a prime.

It is a super-2 number, since 2×991897897² = 1967722876146045218, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (991897397) 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, 3158754 + ... + 3159067.

It is an arithmetic number, because the mean of its divisors is an integer number (249553969).

Almost surely, 2^991897897 is an apocalyptic number.

It is an amenable number.

991897897 is a deficient number, since it is larger than the sum of its proper divisors (6317979).

991897897 is a wasteful number, since it uses less digits than its factorization.

991897897 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6317978.

The product of its digits is 20575296, while the sum is 67.

The square root of 991897897 is about 31494.4105675912. The cubic root of 991897897 is about 997.2919722052.

The spelling of 991897897 in words is "nine hundred ninety-one million, eight hundred ninety-seven thousand, eight hundred ninety-seven".