991000000181 has 2 divisors, whose sum is σ = 991000000182. Its totient is φ = 991000000180.

The previous prime is 991000000139. The next prime is 991000000201. The reversal of 991000000181 is 181000000199.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 973567023025 + 17432977156 = 986695^2 + 132034^2 .

It is a cyclic number.

It is not a de Polignac number, because 991000000181 - 2¹⁴ = 990999983797 is a prime.

It is a super-2 number, since 2×991000000181² (a number of 25 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (991000000681) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495500000090 + 495500000091.

It is an arithmetic number, because the mean of its divisors is an integer number (495500000091).

Almost surely, 2^991000000181 is an apocalyptic number.

It is an amenable number.

991000000181 is a deficient number, since it is larger than the sum of its proper divisors (1).

991000000181 is an equidigital number, since it uses as much as digits as its factorization.

991000000181 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 648, while the sum is 29.

The spelling of 991000000181 in words is "nine hundred ninety-one billion, one hundred eighty-one", and thus it is an aban number.