209995991 has 2 divisors, whose sum is σ = 209995992. Its totient is φ = 209995990.

The previous prime is 209995967. The next prime is 209995993. The reversal of 209995991 is 199599902.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 209995991 - 2¹⁴ = 209979607 is a prime.

Together with 209995993, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (209995993) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104997995 + 104997996.

It is an arithmetic number, because the mean of its divisors is an integer number (104997996).

Almost surely, 2^209995991 is an apocalyptic number.

209995991 is a deficient number, since it is larger than the sum of its proper divisors (1).

209995991 is an equidigital number, since it uses as much as digits as its factorization.

209995991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 590490, while the sum is 53.

The square root of 209995991 is about 14491.2384218879. The cubic root of 209995991 is about 594.3884128422.

The spelling of 209995991 in words is "two hundred nine million, nine hundred ninety-five thousand, nine hundred ninety-one".