1991308121 has 8 divisors (see below), whose sum is σ = 2186724288. Its totient is φ = 1798290000.

The previous prime is 1991308117. The next prime is 1991308147. The reversal of 1991308121 is 1218031991.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 1991308121 - 2² = 1991308117 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991308321) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 597770 + ... + 601091.

It is an arithmetic number, because the mean of its divisors is an integer number (273340536).

Almost surely, 2^1991308121 is an apocalyptic number.

1991308121 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

1991308121 is a deficient number, since it is larger than the sum of its proper divisors (195416167).

1991308121 is a wasteful number, since it uses less digits than its factorization.

1991308121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1199023.

The product of its (nonzero) digits is 3888, while the sum is 35.

The square root of 1991308121 is about 44624.0755758593. The cubic root of 1991308121 is about 1258.0932192324.

The spelling of 1991308121 in words is "one billion, nine hundred ninety-one million, three hundred eight thousand, one hundred twenty-one".