1991252161 has 4 divisors (see below), whose sum is σ = 1999584000. Its totient is φ = 1982920324.

The previous prime is 1991252141. The next prime is 1991252167. The reversal of 1991252161 is 1612521991.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 1612521991 = 10273 ⋅156967.

It is a cyclic number.

It is not a de Polignac number, because 1991252161 - 2²⁹ = 1454381249 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 1991252161.

It is not an unprimeable number, because it can be changed into a prime (1991252167) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 4165561 + ... + 4166038.

It is an arithmetic number, because the mean of its divisors is an integer number (499896000).

Almost surely, 2^1991252161 is an apocalyptic number.

It is an amenable number.

1991252161 is a deficient number, since it is larger than the sum of its proper divisors (8331839).

1991252161 is an equidigital number, since it uses as much as digits as its factorization.

1991252161 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 8331838.

The product of its digits is 9720, while the sum is 37.

The square root of 1991252161 is about 44623.4485556641. The cubic root of 1991252161 is about 1258.0814340888.

The spelling of 1991252161 in words is "one billion, nine hundred ninety-one million, two hundred fifty-two thousand, one hundred sixty-one".