65991999 has 4 divisors (see below), whose sum is σ = 87989336. Its totient is φ = 43994664.

The previous prime is 65991953. The next prime is 65992013. The reversal of 65991999 is 99919956.

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

It is not a de Polignac number, because 65991999 - 2⁹ = 65991487 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (65991949) 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, 10998664 + ... + 10998669.

It is an arithmetic number, because the mean of its divisors is an integer number (21997334).

Almost surely, 2^65991999 is an apocalyptic number.

65991999 is a deficient number, since it is larger than the sum of its proper divisors (21997337).

65991999 is a wasteful number, since it uses less digits than its factorization.

65991999 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 21997336.

The product of its digits is 1771470, while the sum is 57.

The square root of 65991999 is about 8123.5459622015. The cubic root of 65991999 is about 404.1076711187.

The spelling of 65991999 in words is "sixty-five million, nine hundred ninety-one thousand, nine hundred ninety-nine".