999156721 has 2 divisors, whose sum is σ = 999156722.
Its totient is φ = 999156720.
The previous prime is 999156713. The next prime is 999156727. The reversal of 999156721 is 127651999.
It is the 12905-th star number.
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 860835600 + 138321121 = 29340^2 + 11761^2
It is an emirp because it is prime and its reverse (127651999) is a distict prime.
It is a cyclic number.
It is not a de Polignac number, because 999156721 - 23 = 999156713 is a prime.
It is a Chen prime.
It is not a weakly prime, because it can be changed into another prime (999156727) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 499578360 + 499578361.
It is an arithmetic number, because the mean of its divisors is an integer number (499578361).
Almost surely, 2999156721 is an apocalyptic number.
It is an amenable number.
999156721 is a deficient number, since it is larger than the sum of its proper divisors (1).
999156721 is an equidigital number, since it uses as much as digits as its factorization.
999156721 is an evil number, because the sum of its binary digits is even.
The product of its digits is 306180, while the sum is 49.
The square root of 999156721 is about 31609.4403778365.
The cubic root of 999156721 is about 999.7188279497.
The spelling of 999156721 in words is "nine hundred ninety-nine million, one hundred fifty-six thousand, seven hundred twenty-one".