999557721 has 12 divisors (see below), whose sum is σ = 1528735572. Its totient is φ = 627173376.

The previous prime is 999557717. The next prime is 999557723. The reversal of 999557721 is 127755999.

It can be written as a sum of positive squares in 2 ways, for example, as 868775625 + 130782096 = 29475^2 + 11436^2 .

It is not a de Polignac number, because 999557721 - 2² = 999557717 is a prime.

It is a super-2 number, since 2×999557721² = 1998231275221427682, which contains 22 as substring.

It is not an unprimeable number, because it can be changed into a prime (999557723) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 3266376 + ... + 3266681.

It is an arithmetic number, because the mean of its divisors is an integer number (127394631).

Almost surely, 2^999557721 is an apocalyptic number.

It is an amenable number.

999557721 is a deficient number, since it is larger than the sum of its proper divisors (529177851).

999557721 is a wasteful number, since it uses less digits than its factorization.

999557721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 6533080 (or 6533077 counting only the distinct ones).

The product of its digits is 1786050, while the sum is 54.

The square root of 999557721 is about 31615.7827832872. The cubic root of 999557721 is about 999.8525519268.

The spelling of 999557721 in words is "nine hundred ninety-nine million, five hundred fifty-seven thousand, seven hundred twenty-one".