66815971 has 4 divisors (see below), whose sum is σ = 69120000. Its totient is φ = 64511944.

The previous prime is 66815953. The next prime is 66815977. The reversal of 66815971 is 17951866.

It is a happy number.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 17951866 = 2 ⋅8975933.

It is a cyclic number.

It is not a de Polignac number, because 66815971 - 2⁹ = 66815459 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66815977) 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, 1151971 + ... + 1152028.

It is an arithmetic number, because the mean of its divisors is an integer number (17280000).

Almost surely, 2^66815971 is an apocalyptic number.

66815971 is a deficient number, since it is larger than the sum of its proper divisors (2304029).

66815971 is a wasteful number, since it uses less digits than its factorization.

66815971 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2304028.

The product of its digits is 90720, while the sum is 43.

The square root of 66815971 is about 8174.1036817501. The cubic root of 66815971 is about 405.7826070518.

The spelling of 66815971 in words is "sixty-six million, eight hundred fifteen thousand, nine hundred seventy-one".