991199081 has 2 divisors, whose sum is σ = 991199082. Its totient is φ = 991199080.

The previous prime is 991199071. The next prime is 991199117. The reversal of 991199081 is 180991199.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 691216681 + 299982400 = 26291^2 + 17320^2 .

It is an emirp because it is prime and its reverse (180991199) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 991199081 - 2¹⁴ = 991182697 is a prime.

It is a super-2 number, since 2×991199081² = 1964951236350489122, which contains 22 as substring.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (991199071) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495599540 + 495599541.

It is an arithmetic number, because the mean of its divisors is an integer number (495599541).

Almost surely, 2^991199081 is an apocalyptic number.

It is an amenable number.

991199081 is a deficient number, since it is larger than the sum of its proper divisors (1).

991199081 is an equidigital number, since it uses as much as digits as its factorization.

991199081 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 52488, while the sum is 47.

The square root of 991199081 is about 31483.3143267986. The cubic root of 991199081 is about 997.0577117638.

The spelling of 991199081 in words is "nine hundred ninety-one million, one hundred ninety-nine thousand, eighty-one".