66006991 has 4 divisors (see below), whose sum is σ = 66043512. Its totient is φ = 65970472.

The previous prime is 66006989. The next prime is 66007031. The reversal of 66006991 is 19960066.

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 66006991 - 2¹ = 66006989 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 66006991.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66006491) 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, 15400 + ... + 19213.

It is an arithmetic number, because the mean of its divisors is an integer number (16510878).

Almost surely, 2^66006991 is an apocalyptic number.

66006991 is a deficient number, since it is larger than the sum of its proper divisors (36521).

66006991 is a wasteful number, since it uses less digits than its factorization.

66006991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 36520.

The product of its (nonzero) digits is 17496, while the sum is 37.

The square root of 66006991 is about 8124.4686595494. The cubic root of 66006991 is about 404.1382704014.

The spelling of 66006991 in words is "sixty-six million, six thousand, nine hundred ninety-one".