1668795781 has 2 divisors, whose sum is σ = 1668795782. Its totient is φ = 1668795780.

The previous prime is 1668795773. The next prime is 1668795827. The reversal of 1668795781 is 1875978661.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 1356743556 + 312052225 = 36834^2 + 17665^2 .

It is a cyclic number.

It is not a de Polignac number, because 1668795781 - 2³ = 1668795773 is a prime.

It is a super-2 number, since 2×1668795781² = 5569758717366799922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1668795761) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 834397890 + 834397891.

It is an arithmetic number, because the mean of its divisors is an integer number (834397891).

Almost surely, 2^1668795781 is an apocalyptic number.

It is an amenable number.

1668795781 is a deficient number, since it is larger than the sum of its proper divisors (1).

1668795781 is an equidigital number, since it uses as much as digits as its factorization.

1668795781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 5080320, while the sum is 58.

The square root of 1668795781 is about 40850.8969424173. The cubic root of 1668795781 is about 1186.1357554989.

It can be divided in two parts, 1668 and 795781, that added together give a square (797449 = 893²).

The spelling of 1668795781 in words is "one billion, six hundred sixty-eight million, seven hundred ninety-five thousand, seven hundred eighty-one".