1991309121 has 12 divisors (see below), whose sum is σ = 2884629072. Its totient is φ = 1323711576.

The previous prime is 1991309107. The next prime is 1991309129. The reversal of 1991309121 is 1219031991.

It is not a de Polignac number, because 1991309121 - 2¹⁰ = 1991308097 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1991309129) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 315691 + ... + 321936.

It is an arithmetic number, because the mean of its divisors is an integer number (240385756).

Almost surely, 2^1991309121 is an apocalyptic number.

It is an amenable number.

1991309121 is a deficient number, since it is larger than the sum of its proper divisors (893319951).

1991309121 is a wasteful number, since it uses less digits than its factorization.

1991309121 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 637980 (or 637977 counting only the distinct ones).

The product of its (nonzero) digits is 4374, while the sum is 36.

The square root of 1991309121 is about 44624.0867805718. The cubic root of 1991309121 is about 1258.0934298298.

The spelling of 1991309121 in words is "one billion, nine hundred ninety-one million, three hundred nine thousand, one hundred twenty-one".