1991845326181 has 2 divisors, whose sum is σ = 1991845326182. Its totient is φ = 1991845326180.

The previous prime is 1991845326143. The next prime is 1991845326269. The reversal of 1991845326181 is 1816235481991.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1496546075556 + 495299250625 = 1223334^2 + 703775^2 .

It is a cyclic number.

It is not a de Polignac number, because 1991845326181 - 2¹⁵ = 1991845293413 is a prime.

It is a super-2 number, since 2×1991845326181² (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 (1991845321181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 995922663090 + 995922663091.

It is an arithmetic number, because the mean of its divisors is an integer number (995922663091).

Almost surely, 2^{1991845326181} is an apocalyptic number.

It is an amenable number.

1991845326181 is a deficient number, since it is larger than the sum of its proper divisors (1).

1991845326181 is an equidigital number, since it uses as much as digits as its factorization.

1991845326181 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 3732480, while the sum is 58.

The spelling of 1991845326181 in words is "one trillion, nine hundred ninety-one billion, eight hundred forty-five million, three hundred twenty-six thousand, one hundred eighty-one".