6663816529921 has 16 divisors (see below), whose sum is σ = 6800278708368. Its totient is φ = 6527757600000.

The previous prime is 6663816529919. The next prime is 6663816529949. The reversal of 6663816529921 is 1299256183666.

It can be written as a sum of positive squares in 8 ways, for example, as 449570250000 + 6214246279921 = 670500^2 + 2492839^2 .

It is a cyclic number.

It is not a de Polignac number, because 6663816529921 - 2¹ = 6663816529919 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6663816529961) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 126901171 + ... + 126953671.

It is an arithmetic number, because the mean of its divisors is an integer number (425017419273).

Almost surely, 2^{6663816529921} is an apocalyptic number.

It is an amenable number.

6663816529921 is a deficient number, since it is larger than the sum of its proper divisors (136462178447).

6663816529921 is a wasteful number, since it uses less digits than its factorization.

6663816529921 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 56292.

The product of its digits is 50388480, while the sum is 64.

The spelling of 6663816529921 in words is "six trillion, six hundred sixty-three billion, eight hundred sixteen million, five hundred twenty-nine thousand, nine hundred twenty-one".