66718921 has 4 divisors (see below), whose sum is σ = 67010500. Its totient is φ = 66427344.

The previous prime is 66718919. The next prime is 66718957. The reversal of 66718921 is 12981766.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 26574025 + 40144896 = 5155^2 + 6336^2 .

It is a cyclic number.

It is not a de Polignac number, because 66718921 - 2¹ = 66718919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66718961) 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, 145446 + ... + 145903.

It is an arithmetic number, because the mean of its divisors is an integer number (16752625).

Almost surely, 2^66718921 is an apocalyptic number.

It is an amenable number.

66718921 is a deficient number, since it is larger than the sum of its proper divisors (291579).

66718921 is a wasteful number, since it uses less digits than its factorization.

66718921 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 291578.

The product of its digits is 36288, while the sum is 40.

The square root of 66718921 is about 8168.1650938262. The cubic root of 66718921 is about 405.5860458412.

The spelling of 66718921 in words is "sixty-six million, seven hundred eighteen thousand, nine hundred twenty-one".