209123391643781 has 2 divisors, whose sum is σ = 209123391643782. Its totient is φ = 209123391643780.

The previous prime is 209123391643711. The next prime is 209123391643783. The reversal of 209123391643781 is 187346193321902.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 198205429317025 + 10917962326756 = 14078545^2 + 3304234^2 .

It is a cyclic number.

It is not a de Polignac number, because 209123391643781 - 2¹⁰ = 209123391642757 is a prime.

It is a super-2 number, since 2×209123391643781² (a number of 29 digits) contains 22 as substring.

Together with 209123391643783, it forms a pair of twin primes.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 209123391643781.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (209123391643783) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 104561695821890 + 104561695821891.

It is an arithmetic number, because the mean of its divisors is an integer number (104561695821891).

Almost surely, 2^{209123391643781} is an apocalyptic number.

It is an amenable number.

209123391643781 is a deficient number, since it is larger than the sum of its proper divisors (1).

209123391643781 is an equidigital number, since it uses as much as digits as its factorization.

209123391643781 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 11757312, while the sum is 59.

The spelling of 209123391643781 in words is "two hundred nine trillion, one hundred twenty-three billion, three hundred ninety-one million, six hundred forty-three thousand, seven hundred eighty-one".