1668311681 has 4 divisors (see below), whose sum is σ = 1725839700. Its totient is φ = 1610783664.

The previous prime is 1668311657. The next prime is 1668311699. The reversal of 1668311681 is 1861138661.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1861138661 = 31 ⋅60036731.

It can be written as a sum of positive squares in 2 ways, for example, as 442681600 + 1225630081 = 21040^2 + 35009^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-1668311681 is a prime.

It is a super-2 number, since 2×1668311681² = 5566527729922091522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1668311621) 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 in 3 ways as a sum of consecutive naturals, for example, 28763966 + ... + 28764023.

It is an arithmetic number, because the mean of its divisors is an integer number (431459925).

Almost surely, 2^1668311681 is an apocalyptic number.

It is an amenable number.

1668311681 is a deficient number, since it is larger than the sum of its proper divisors (57528019).

1668311681 is an equidigital number, since it uses as much as digits as its factorization.

1668311681 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 57528018.

The product of its digits is 41472, while the sum is 41.

The square root of 1668311681 is about 40844.9713061473. The cubic root of 1668311681 is about 1186.0210492621.

The spelling of 1668311681 in words is "one billion, six hundred sixty-eight million, three hundred eleven thousand, six hundred eighty-one".