66139999 has 4 divisors (see below), whose sum is σ = 66164560. Its totient is φ = 66115440.

The previous prime is 66139993. The next prime is 66140027. The reversal of 66139999 is 99993166.

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 66139999 - 2⁹ = 66139487 is a prime.

It is a Duffinian number.

66139999 is a modest number, since divided by 9999 gives 6613 as remainder.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66139993) 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, 7662 + ... + 13819.

It is an arithmetic number, because the mean of its divisors is an integer number (16541140).

Almost surely, 2^66139999 is an apocalyptic number.

66139999 is a deficient number, since it is larger than the sum of its proper divisors (24561).

66139999 is a wasteful number, since it uses less digits than its factorization.

66139999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 24560.

The product of its digits is 708588, while the sum is 52.

The square root of 66139999 is about 8132.6501830584. The cubic root of 66139999 is about 404.4095424643.

The spelling of 66139999 in words is "sixty-six million, one hundred thirty-nine thousand, nine hundred ninety-nine".