209404991 has 2 divisors, whose sum is σ = 209404992. Its totient is φ = 209404990.

The previous prime is 209404981. The next prime is 209405011. The reversal of 209404991 is 199404902.

It is a happy number.

It is a weak prime.

It is a cyclic number.

It is not a de Polignac number, because 209404991 - 2¹⁸ = 209142847 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (209404931) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104702495 + 104702496.

It is an arithmetic number, because the mean of its divisors is an integer number (104702496).

Almost surely, 2^209404991 is an apocalyptic number.

209404991 is a deficient number, since it is larger than the sum of its proper divisors (1).

209404991 is an equidigital number, since it uses as much as digits as its factorization.

209404991 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 23328, while the sum is 38.

The square root of 209404991 is about 14470.8324224973. The cubic root of 209404991 is about 593.8302853430.

The spelling of 209404991 in words is "two hundred nine million, four hundred four thousand, nine hundred ninety-one".