1668718820521 has 9 divisors (see below), whose sum is σ = 1676334792933. Its totient is φ = 1661137310880.

The previous prime is 1668718820477. The next prime is 1668718820609. The reversal of 1668718820521 is 1250288178661.

The square root of 1668718820521 is 1291789.

It is a perfect power (a square), and thus also a powerful number.

It can be written as a sum of positive squares in 4 ways, for example, as 1448626480921 + 220092339600 = 1203589^2 + 469140^2 .

It is not a de Polignac number, because 1668718820521 - 2¹⁵ = 1668718787753 is a prime.

It is a super-2 number, since 2×1668718820521² (a number of 25 digits) contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (1668718820921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 8 ways as a sum of consecutive naturals, for example, 295816861 + ... + 295822501.

It is an arithmetic number, because the mean of its divisors is an integer number (186259421437).

Almost surely, 2^{1668718820521} is an apocalyptic number.

1668718820521 is the 1291789-th square number.

1668718820521 is the 645895-th centered octagonal number.

It is an amenable number.

1668718820521 is a deficient number, since it is larger than the sum of its proper divisors (7615972412).

1668718820521 is an frugal number, since it uses more digits than its factorization.

1668718820521 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11740 (or 5870 counting only the distinct ones).

The product of its (nonzero) digits is 2580480, while the sum is 55.

The spelling of 1668718820521 in words is "one trillion, six hundred sixty-eight billion, seven hundred eighteen million, eight hundred twenty thousand, five hundred twenty-one".