66999999 has 24 divisors (see below), whose sum is σ = 98654080. Its totient is φ = 40415760.

The previous prime is 66999997. The next prime is 67000019. The reversal of 66999999 is 99999966.

It is not a de Polignac number, because 66999999 - 2¹ = 66999997 is a prime.

It is a Duffinian number.

66999999 is a modest number, since divided by 9999 gives 6699 as remainder.

It is a plaindrome in base 10.

It is a zygodrome in base 10.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66999997) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 137334 + ... + 137820.

Almost surely, 2^66999999 is an apocalyptic number.

66999999 is a deficient number, since it is larger than the sum of its proper divisors (31654081).

66999999 is a wasteful number, since it uses less digits than its factorization.

66999999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 891 (or 880 counting only the distinct ones).

The product of its digits is 19131876, while the sum is 66.

The square root of 66999999 is about 8185.3527107877. The cubic root of 66999999 is about 406.1548080239.

The spelling of 66999999 in words is "sixty-six million, nine hundred ninety-nine thousand, nine hundred ninety-nine".