1668406681 has 4 divisors (see below), whose sum is σ = 1670132992. Its totient is φ = 1666680372.

The previous prime is 1668406667. The next prime is 1668406697. The reversal of 1668406681 is 1866048661.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 1668406681 - 2¹³ = 1668398489 is a prime.

It is a super-2 number, since 2×1668406681² = 5567161706410871522, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1668406601) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 861705 + ... + 863638.

It is an arithmetic number, because the mean of its divisors is an integer number (417533248).

Almost surely, 2^1668406681 is an apocalyptic number.

It is an amenable number.

1668406681 is a deficient number, since it is larger than the sum of its proper divisors (1726311).

1668406681 is an equidigital number, since it uses as much as digits as its factorization.

1668406681 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1726310.

The product of its (nonzero) digits is 331776, while the sum is 46.

The square root of 1668406681 is about 40846.1342234489. The cubic root of 1668406681 is about 1186.0435610150.

The spelling of 1668406681 in words is "one billion, six hundred sixty-eight million, four hundred six thousand, six hundred eighty-one".