209805221993 has 2 divisors, whose sum is σ = 209805221994. Its totient is φ = 209805221992.

The previous prime is 209805221939. The next prime is 209805222037. The reversal of 209805221993 is 399122508902.

Together with previous prime (209805221939) it forms an Ormiston pair, because they use the same digits, order apart.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 137365114384 + 72440107609 = 370628^2 + 269147^2 .

It is a cyclic number.

It is not a de Polignac number, because 209805221993 - 2¹⁴ = 209805205609 is a prime.

It is not a weakly prime, because it can be changed into another prime (209805221903) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104902610996 + 104902610997.

It is an arithmetic number, because the mean of its divisors is an integer number (104902610997).

Almost surely, 2^209805221993 is an apocalyptic number.

It is an amenable number.

209805221993 is a deficient number, since it is larger than the sum of its proper divisors (1).

209805221993 is an equidigital number, since it uses as much as digits as its factorization.

209805221993 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 699840, while the sum is 50.

The spelling of 209805221993 in words is "two hundred nine billion, eight hundred five million, two hundred twenty-one thousand, nine hundred ninety-three".