9991581 has 4 divisors (see below), whose sum is σ = 13322112. Its totient is φ = 6661052.

The previous prime is 9991571. The next prime is 9991603. The reversal of 9991581 is 1851999.

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: 1851999 = 3 ⋅617333.

It is a cyclic number.

It is not a de Polignac number, because 9991581 - 2¹⁰ = 9990557 is a prime.

It is a super-2 number, since 2×9991581² = 199663381759122, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (9991571) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1665261 + ... + 1665266.

It is an arithmetic number, because the mean of its divisors is an integer number (3330528).

Almost surely, 2^9991581 is an apocalyptic number.

It is an amenable number.

9991581 is a deficient number, since it is larger than the sum of its proper divisors (3330531).

9991581 is a wasteful number, since it uses less digits than its factorization.

9991581 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3330530.

The product of its digits is 29160, while the sum is 42.

The square root of 9991581 is about 3160.9462190933. The cubic root of 9991581 is about 215.3829914091.

The spelling of 9991581 in words is "nine million, nine hundred ninety-one thousand, five hundred eighty-one".