991090991901 has 4 divisors (see below), whose sum is σ = 1321454655872. Its totient is φ = 660727327932.

The previous prime is 991090991837. The next prime is 991090991903. The reversal of 991090991901 is 109199090199.

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: 109199090199 = 3 ⋅36399696733.

It is not a de Polignac number, because 991090991901 - 2⁶ = 991090991837 is a prime.

It is a super-2 number, since 2×991090991901² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (991090991903) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 165181831981 + ... + 165181831986.

It is an arithmetic number, because the mean of its divisors is an integer number (330363663968).

Almost surely, 2^991090991901 is an apocalyptic number.

It is an amenable number.

991090991901 is a deficient number, since it is larger than the sum of its proper divisors (330363663971).

991090991901 is a wasteful number, since it uses less digits than its factorization.

991090991901 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 330363663970.

The product of its (nonzero) digits is 531441, while the sum is 57.

The spelling of 991090991901 in words is "nine hundred ninety-one billion, ninety million, nine hundred ninety-one thousand, nine hundred one".