987817991 has 4 divisors (see below), whose sum is σ = 994359984. Its totient is φ = 981276000.

The previous prime is 987817949. The next prime is 987818011. The reversal of 987817991 is 199718789.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 199718789 = 43 ⋅4644623.

It is a cyclic number.

It is not a de Polignac number, because 987817991 - 2⁶ = 987817927 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 987817991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (987817931) 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, 3270770 + ... + 3271071.

It is an arithmetic number, because the mean of its divisors is an integer number (248589996).

Almost surely, 2^987817991 is an apocalyptic number.

987817991 is a deficient number, since it is larger than the sum of its proper divisors (6541993).

987817991 is a wasteful number, since it uses less digits than its factorization.

987817991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6541992.

The product of its digits is 2286144, while the sum is 59.

The square root of 987817991 is about 31429.5719188156. The cubic root of 987817991 is about 995.9227287865.

The spelling of 987817991 in words is "nine hundred eighty-seven million, eight hundred seventeen thousand, nine hundred ninety-one".