991868209 has 2 divisors, whose sum is σ = 991868210. Its totient is φ = 991868208.

The previous prime is 991868197. The next prime is 991868221. The reversal of 991868209 is 902868199.

It is a balanced prime because it is at equal distance from previous prime (991868197) and next prime (991868221).

It can be written as a sum of positive squares in only one way, i.e., 917908209 + 73960000 = 30297^2 + 8600^2 .

It is a cyclic number.

It is not a de Polignac number, because 991868209 - 2¹⁷ = 991737137 is a prime.

It is not a weakly prime, because it can be changed into another prime (991868809) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 495934104 + 495934105.

It is an arithmetic number, because the mean of its divisors is an integer number (495934105).

Almost surely, 2^991868209 is an apocalyptic number.

It is an amenable number.

991868209 is a deficient number, since it is larger than the sum of its proper divisors (1).

991868209 is an equidigital number, since it uses as much as digits as its factorization.

991868209 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 559872, while the sum is 52.

The square root of 991868209 is about 31493.9392423368. The cubic root of 991868209 is about 997.2820222901.

The spelling of 991868209 in words is "nine hundred ninety-one million, eight hundred sixty-eight thousand, two hundred nine".