66721667 has 4 divisors (see below), whose sum is σ = 66949680. Its totient is φ = 66493656.

The previous prime is 66721661. The next prime is 66721679. The reversal of 66721667 is 76612766.

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 66721667 - 2¹⁶ = 66656131 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66721661) 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, 113567 + ... + 114152.

It is an arithmetic number, because the mean of its divisors is an integer number (16737420).

Almost surely, 2^66721667 is an apocalyptic number.

66721667 is a deficient number, since it is larger than the sum of its proper divisors (228013).

66721667 is a wasteful number, since it uses less digits than its factorization.

66721667 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 228012.

The product of its digits is 127008, while the sum is 41.

The square root of 66721667 is about 8168.3331837040. Note that the first 3 decimals coincide. The cubic root of 66721667 is about 405.5916100999.

The spelling of 66721667 in words is "sixty-six million, seven hundred twenty-one thousand, six hundred sixty-seven".