90991981991 has 4 divisors (see below), whose sum is σ = 90993225984. Its totient is φ = 90990738000.

The previous prime is 90991981943. The next prime is 90991982033. The reversal of 90991981991 is 19918919909.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19918919909 = 7 ⋅2845559987.

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-90991981991 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (90991980991) 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, 504935 + ... + 661016.

It is an arithmetic number, because the mean of its divisors is an integer number (22748306496).

Almost surely, 2^90991981991 is an apocalyptic number.

90991981991 is a deficient number, since it is larger than the sum of its proper divisors (1243993).

90991981991 is a wasteful number, since it uses less digits than its factorization.

90991981991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1243992.

The product of its (nonzero) digits is 4251528, while the sum is 65.

The spelling of 90991981991 in words is "ninety billion, nine hundred ninety-one million, nine hundred eighty-one thousand, nine hundred ninety-one".