66681391 has 8 divisors (see below), whose sum is σ = 77829120. Its totient is φ = 55939128.

The previous prime is 66681383. The next prime is 66681401. The reversal of 66681391 is 19318666.

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

It is not a de Polignac number, because 66681391 - 2³ = 66681383 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 (66681371) 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, 101011 + ... + 101668.

It is an arithmetic number, because the mean of its divisors is an integer number (9728640).

Almost surely, 2^66681391 is an apocalyptic number.

66681391 is a deficient number, since it is larger than the sum of its proper divisors (11147729).

66681391 is a wasteful number, since it uses less digits than its factorization.

66681391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 202733.

The product of its digits is 46656, while the sum is 40.

The square root of 66681391 is about 8165.8674370822. The cubic root of 66681391 is about 405.5099829639.

The spelling of 66681391 in words is "sixty-six million, six hundred eighty-one thousand, three hundred ninety-one".