3991995999721 has 16 divisors (see below), whose sum is σ = 4040075378304. Its totient is φ = 3944238787584.

The previous prime is 3991995999713. The next prime is 3991995999743. The reversal of 3991995999721 is 1279995991993.

It is a happy number.

3991995999721 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a cyclic number.

It is not a de Polignac number, because 3991995999721 - 2³ = 3991995999713 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (3991995991721) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 39045150 + ... + 39147256.

It is an arithmetic number, because the mean of its divisors is an integer number (252504711144).

Almost surely, 2^{3991995999721} is an apocalyptic number.

It is an amenable number.

3991995999721 is a deficient number, since it is larger than the sum of its proper divisors (48079378583).

3991995999721 is a wasteful number, since it uses less digits than its factorization.

3991995999721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 103680.

The product of its digits is 1004423490, while the sum is 82.

The spelling of 3991995999721 in words is "three trillion, nine hundred ninety-one billion, nine hundred ninety-five million, nine hundred ninety-nine thousand, seven hundred twenty-one".