1209172755781 has 2 divisors, whose sum is σ = 1209172755782. Its totient is φ = 1209172755780.

The previous prime is 1209172755779. The next prime is 1209172755979. The reversal of 1209172755781 is 1875572719021.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 816086390625 + 393086365156 = 903375^2 + 626966^2 .

It is a cyclic number.

It is not a de Polignac number, because 1209172755781 - 2¹ = 1209172755779 is a prime.

It is a super-2 number, since 2×1209172755781² (a number of 25 digits) contains 22 as substring.

Together with 1209172755779, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1209172755701) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 604586377890 + 604586377891.

It is an arithmetic number, because the mean of its divisors is an integer number (604586377891).

Almost surely, 2^{1209172755781} is an apocalyptic number.

It is an amenable number.

1209172755781 is a deficient number, since it is larger than the sum of its proper divisors (1).

1209172755781 is an equidigital number, since it uses as much as digits as its factorization.

1209172755781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2469600, while the sum is 55.

The spelling of 1209172755781 in words is "one trillion, two hundred nine billion, one hundred seventy-two million, seven hundred fifty-five thousand, seven hundred eighty-one".