66715991 has 4 divisors (see below), whose sum is σ = 67306512. Its totient is φ = 66125472.

The previous prime is 66715967. The next prime is 66716003. The reversal of 66715991 is 19951766.

It is a happy number.

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 66715991 - 2²² = 62521687 is a prime.

It is a super-2 number, since 2×66715991² = 8902046910224162, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66715951) 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, 295091 + ... + 295316.

It is an arithmetic number, because the mean of its divisors is an integer number (16826628).

Almost surely, 2^66715991 is an apocalyptic number.

66715991 is a deficient number, since it is larger than the sum of its proper divisors (590521).

66715991 is a wasteful number, since it uses less digits than its factorization.

66715991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 590520.

The product of its digits is 102060, while the sum is 44.

The square root of 66715991 is about 8167.9857370101. The cubic root of 66715991 is about 405.5801085724.

The spelling of 66715991 in words is "sixty-six million, seven hundred fifteen thousand, nine hundred ninety-one".