191666861 has 4 divisors (see below), whose sum is σ = 191796732. Its totient is φ = 191536992.

The previous prime is 191666821. The next prime is 191666879. The reversal of 191666861 is 168666191.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 168666191 = 59 ⋅2858749.

It can be written as a sum of positive squares in 2 ways, for example, as 145684900 + 45981961 = 12070^2 + 6781^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-191666861 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 (191666801) 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, 62696 + ... + 65681.

It is an arithmetic number, because the mean of its divisors is an integer number (47949183).

Almost surely, 2^191666861 is an apocalyptic number.

It is an amenable number.

191666861 is a deficient number, since it is larger than the sum of its proper divisors (129871).

191666861 is a wasteful number, since it uses less digits than its factorization.

191666861 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 129870.

The product of its digits is 93312, while the sum is 44.

The square root of 191666861 is about 13844.3801233569. The cubic root of 191666861 is about 576.5659755291.

The spelling of 191666861 in words is "one hundred ninety-one million, six hundred sixty-six thousand, eight hundred sixty-one".