1991230121 has 8 divisors (see below), whose sum is σ = 1999563144. Its totient is φ = 1982914560.

The previous prime is 1991230063. The next prime is 1991230123. The reversal of 1991230121 is 1210321991.

It can be written as a sum of positive squares in 4 ways, for example, as 364237225 + 1626992896 = 19085^2 + 40336^2 .

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 1991230121 - 2⁶ = 1991230057 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1991230123) 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, 255401 + ... + 263081.

It is an arithmetic number, because the mean of its divisors is an integer number (249945393).

Almost surely, 2^1991230121 is an apocalyptic number.

It is an amenable number.

1991230121 is a deficient number, since it is larger than the sum of its proper divisors (8333023).

1991230121 is an equidigital number, since it uses as much as digits as its factorization.

1991230121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8731.

The product of its (nonzero) digits is 972, while the sum is 29.

The square root of 1991230121 is about 44623.2015996163. The cubic root of 1991230121 is about 1258.0767924170.

The spelling of 1991230121 in words is "one billion, nine hundred ninety-one million, two hundred thirty thousand, one hundred twenty-one".