1993955805781 has 2 divisors, whose sum is σ = 1993955805782. Its totient is φ = 1993955805780.

The previous prime is 1993955805773. The next prime is 1993955805817. The reversal of 1993955805781 is 1875085593991.

Together with next prime (1993955805817) it forms an Ormiston pair, because they use the same digits, order apart.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1640922570225 + 353033235556 = 1280985^2 + 594166^2 .

It is a cyclic number.

It is not a de Polignac number, because 1993955805781 - 2³ = 1993955805773 is a prime.

It is a super-2 number, since 2×1993955805781² (a number of 25 digits) contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 1993955805781.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1993955805701) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 996977902890 + 996977902891.

It is an arithmetic number, because the mean of its divisors is an integer number (996977902891).

Almost surely, 2^{1993955805781} is an apocalyptic number.

It is an amenable number.

1993955805781 is a deficient number, since it is larger than the sum of its proper divisors (1).

1993955805781 is an equidigital number, since it uses as much as digits as its factorization.

1993955805781 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 122472000, while the sum is 70.

The spelling of 1993955805781 in words is "one trillion, nine hundred ninety-three billion, nine hundred fifty-five million, eight hundred five thousand, seven hundred eighty-one".