66666091 has 4 divisors (see below), whose sum is σ = 66684592. Its totient is φ = 66647592.

The previous prime is 66666071. The next prime is 66666097. The reversal of 66666091 is 19066666.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 19066666 = 2 ⋅9533333.

It is a cyclic number.

It is not a de Polignac number, because 66666091 - 2⁵ = 66666059 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66666097) 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, 1896 + ... + 11701.

It is an arithmetic number, because the mean of its divisors is an integer number (16671148).

Almost surely, 2^66666091 is an apocalyptic number.

66666091 is a deficient number, since it is larger than the sum of its proper divisors (18501).

66666091 is a wasteful number, since it uses less digits than its factorization.

66666091 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 18500.

The product of its (nonzero) digits is 69984, while the sum is 40.

The square root of 66666091 is about 8164.9305569613. The cubic root of 66666091 is about 405.4789659279.

The spelling of 66666091 in words is "sixty-six million, six hundred sixty-six thousand, ninety-one".