99999821 has 2 divisors, whose sum is σ = 99999822.
Its totient is φ = 99999820.
The previous prime is 99999787. The next prime is 99999827. The reversal of 99999821 is 12899999.
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 76825225 + 23174596 = 8765^2 + 4814^2
It is a cyclic number.
It is not a de Polignac number, because 99999821 - 210 = 99998797 is a prime.
It is a nialpdrome in base 10.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (99999827) by changing a digit.
It is a polite number, since it can be written as a sum of consecutive naturals, namely, 49999910 + 49999911.
It is an arithmetic number, because the mean of its divisors is an integer number (49999911).
Almost surely, 299999821 is an apocalyptic number.
It is an amenable number.
99999821 is a deficient number, since it is larger than the sum of its proper divisors (1).
99999821 is an equidigital number, since it uses as much as digits as its factorization.
99999821 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 944784, while the sum is 56.
The square root of 99999821 is about 9999.9910499960.
The cubic root of 99999821 is about 464.1586064130.
The spelling of 99999821 in words is "ninety-nine million, nine hundred ninety-nine thousand, eight hundred twenty-one".