991981983 has 4 divisors (see below), whose sum is σ = 1322642648. Its totient is φ = 661321320.

The previous prime is 991981933. The next prime is 991982027. The reversal of 991981983 is 389189199.

It is a semiprime because it is the product of two primes.

It is not a de Polignac number, because 991981983 - 2⁶ = 991981919 is a prime.

It is a super-2 number, since 2×991981983² = 1968056509193224578, which 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 (991981933) 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, 165330328 + ... + 165330333.

It is an arithmetic number, because the mean of its divisors is an integer number (330660662).

Almost surely, 2^991981983 is an apocalyptic number.

991981983 is a deficient number, since it is larger than the sum of its proper divisors (330660665).

991981983 is a wasteful number, since it uses less digits than its factorization.

991981983 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 330660664.

The product of its digits is 1259712, while the sum is 57.

The square root of 991981983 is about 31495.7454745875. The cubic root of 991981983 is about 997.3201524992.

The spelling of 991981983 in words is "nine hundred ninety-one million, nine hundred eighty-one thousand, nine hundred eighty-three".