191978891 has 8 divisors (see below), whose sum is σ = 207283440. Its totient is φ = 176751072.

The previous prime is 191978873. The next prime is 191978951. The reversal of 191978891 is 198879191.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 191978891 - 2⁶ = 191978827 is a prime.

It is not an unprimeable number, because it can be changed into a prime (191978821) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 13925 + ... + 24038.

It is an arithmetic number, because the mean of its divisors is an integer number (25910430).

Almost surely, 2^191978891 is an apocalyptic number.

191978891 is a deficient number, since it is larger than the sum of its proper divisors (15304549).

191978891 is a wasteful number, since it uses less digits than its factorization.

191978891 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38365.

The product of its digits is 326592, while the sum is 53.

The square root of 191978891 is about 13855.6447341869. The cubic root of 191978891 is about 576.8786853716.

The spelling of 191978891 in words is "one hundred ninety-one million, nine hundred seventy-eight thousand, eight hundred ninety-one".