9939866721 has 32 divisors (see below), whose sum is σ = 13504070400. Its totient is φ = 6502788864.

The previous prime is 9939866711. The next prime is 9939866723. The reversal of 9939866721 is 1276689399.

It is not a de Polignac number, because 9939866721 - 2⁵ = 9939866689 is a prime.

It is not an unprimeable number, because it can be changed into a prime (9939866723) by changing a digit.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 16214811 + ... + 16215423.

It is an arithmetic number, because the mean of its divisors is an integer number (422002200).

Almost surely, 2^9939866721 is an apocalyptic number.

It is an amenable number.

9939866721 is a deficient number, since it is larger than the sum of its proper divisors (3564203679).

9939866721 is a wasteful number, since it uses less digits than its factorization.

9939866721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1145.

The product of its digits is 8817984, while the sum is 60.

The square root of 9939866721 is about 99698.8802394490. The cubic root of 9939866721 is about 2150.1075641876.

The spelling of 9939866721 in words is "nine billion, nine hundred thirty-nine million, eight hundred sixty-six thousand, seven hundred twenty-one".