1991090121 has 8 divisors (see below), whose sum is σ = 2694410784. Its totient is φ = 1307581440.

The previous prime is 1991090089. The next prime is 1991090131. The reversal of 1991090121 is 1210901991.

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

It is not a de Polignac number, because 1991090121 - 2⁵ = 1991090089 is a prime.

It is not an unprimeable number, because it can be changed into a prime (1991090131) 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, 4952760 + ... + 4953161.

It is an arithmetic number, because the mean of its divisors is an integer number (336801348).

Almost surely, 2^1991090121 is an apocalyptic number.

It is an amenable number.

1991090121 is a deficient number, since it is larger than the sum of its proper divisors (703320663).

1991090121 is an equidigital number, since it uses as much as digits as its factorization.

1991090121 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9905991.

The product of its (nonzero) digits is 1458, while the sum is 33.

The square root of 1991090121 is about 44621.6328813727. The cubic root of 1991090121 is about 1258.0473073135.

The spelling of 1991090121 in words is "one billion, nine hundred ninety-one million, ninety thousand, one hundred twenty-one".