191988 has 18 divisors (see below), whose sum is σ = 485394. Its totient is φ = 63984.

The previous prime is 191977. The next prime is 191999. The reversal of 191988 is 889191.

It is an interprime number because it is at equal distance from previous prime (191977) and next prime (191999).

It can be written as a sum of positive squares in only one way, i.e., 191844 + 144 = 438^2 + 12^2 .

It is a tau number, because it is divible by the number of its divisors (18).

It is a Harshad number since it is a multiple of its sum of digits (36), and also a Moran number because the ratio is a prime number: 5333 = 191988 / (1 + 9 + 1 + 9 + 8 + 8).

It is a congruent number.

It is an unprimeable number.

191988 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 2631 + ... + 2702.

2¹⁹¹⁹⁸⁸ is an apocalyptic number.

191988 is a gapful number since it is divisible by the number (18) formed by its first and last digit.

It is an amenable number.

191988 is an abundant number, since it is smaller than the sum of its proper divisors (293406).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

191988 is a wasteful number, since it uses less digits than its factorization.

191988 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5343 (or 5338 counting only the distinct ones).

The product of its digits is 5184, while the sum is 36.

The square root of 191988 is about 438.1643527262. The cubic root of 191988 is about 57.6887809126.

The spelling of 191988 in words is "one hundred ninety-one thousand, nine hundred eighty-eight".