991656181 has 2 divisors, whose sum is σ = 991656182. Its totient is φ = 991656180.

The previous prime is 991656157. The next prime is 991656209. The reversal of 991656181 is 181656199.

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., 828864100 + 162792081 = 28790^2 + 12759^2 .

It is a cyclic number.

It is not a de Polignac number, because 991656181 - 2²⁹ = 454785269 is a prime.

It is a super-2 number, since 2×991656181² = 1966763962631009522, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991656101) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495828090 + 495828091.

It is an arithmetic number, because the mean of its divisors is an integer number (495828091).

Almost surely, 2^991656181 is an apocalyptic number.

It is an amenable number.

991656181 is a deficient number, since it is larger than the sum of its proper divisors (1).

991656181 is an equidigital number, since it uses as much as digits as its factorization.

991656181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 116640, while the sum is 46.

The square root of 991656181 is about 31490.5728909463. The cubic root of 991656181 is about 997.2109554623.

The spelling of 991656181 in words is "nine hundred ninety-one million, six hundred fifty-six thousand, one hundred eighty-one".