66783991 has 4 divisors (see below), whose sum is σ = 66943800. Its totient is φ = 66624184.

The previous prime is 66783989. The next prime is 66784021. The reversal of 66783991 is 19938766.

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 66783991 - 2¹ = 66783989 is a prime.

It is a Smith number, since the sum of its digits (49) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66783901) 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, 79276 + ... + 80113.

It is an arithmetic number, because the mean of its divisors is an integer number (16735950).

Almost surely, 2^66783991 is an apocalyptic number.

66783991 is a deficient number, since it is larger than the sum of its proper divisors (159809).

66783991 is a wasteful number, since it uses less digits than its factorization.

66783991 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 159808.

The product of its digits is 489888, while the sum is 49.

The square root of 66783991 is about 8172.1472698429. The cubic root of 66783991 is about 405.7178570701.

The spelling of 66783991 in words is "sixty-six million, seven hundred eighty-three thousand, nine hundred ninety-one".