999721 has 2 divisors, whose sum is σ = 999722. Its totient is φ = 999720.

The previous prime is 999683. The next prime is 999727. The reversal of 999721 is 127999.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 583696 + 416025 = 764^2 + 645^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-999721 is a prime.

It is a nialpdrome in base 10.

It is not a weakly prime, because it can be changed into another prime (999727) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499860 + 499861.

It is an arithmetic number, because the mean of its divisors is an integer number (499861).

2⁹⁹⁹⁷²¹ is an apocalyptic number.

It is an amenable number.

999721 is a deficient number, since it is larger than the sum of its proper divisors (1).

999721 is an equidigital number, since it uses as much as digits as its factorization.

999721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 10206, while the sum is 37.

The square root of 999721 is about 999.8604902685. The cubic root of 999721 is about 99.9906991350.

The spelling of 999721 in words is "nine hundred ninety-nine thousand, seven hundred twenty-one".