198861991 has 4 divisors (see below), whose sum is σ = 198892584. Its totient is φ = 198831400.

The previous prime is 198861959. The next prime is 198862007. The reversal of 198861991 is 199168891.

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

It is a cyclic number.

It is not a de Polignac number, because 198861991 - 2⁵ = 198861959 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 (198871991) 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, 1240 + ... + 19981.

It is an arithmetic number, because the mean of its divisors is an integer number (49723146).

Almost surely, 2^198861991 is an apocalyptic number.

198861991 is a deficient number, since it is larger than the sum of its proper divisors (30593).

198861991 is an equidigital number, since it uses as much as digits as its factorization.

198861991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 30592.

The product of its digits is 279936, while the sum is 52.

The square root of 198861991 is about 14101.8435319642. The cubic root of 198861991 is about 583.6922510264.

The spelling of 198861991 in words is "one hundred ninety-eight million, eight hundred sixty-one thousand, nine hundred ninety-one".