6643554021 has 48 divisors (see below), whose sum is σ = 10417745520. Its totient is φ = 4055546880.

The previous prime is 6643554019. The next prime is 6643554031. The reversal of 6643554021 is 1204553466.

6643554021 is a `hidden beast` number, since 6 + 64 + 35 + 540 + 21 = 666.

It can be written as a sum of positive squares in 8 ways, for example, as 149450625 + 6494103396 = 12225^2 + 80586^2 .

It is not a de Polignac number, because 6643554021 - 2¹ = 6643554019 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6643554031) by changing a digit.

It is a polite number, since it can be written in 47 ways as a sum of consecutive naturals, for example, 13051915 + ... + 13052423.

It is an arithmetic number, because the mean of its divisors is an integer number (217036365).

Almost surely, 2^6643554021 is an apocalyptic number.

It is an amenable number.

6643554021 is a deficient number, since it is larger than the sum of its proper divisors (3774191499).

6643554021 is a wasteful number, since it uses less digits than its factorization.

6643554021 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1206 (or 1203 counting only the distinct ones).

The product of its (nonzero) digits is 86400, while the sum is 36.

The square root of 6643554021 is about 81507.9997362222. Note that the first 3 decimals coincide. The cubic root of 6643554021 is about 1879.8945561994.

The spelling of 6643554021 in words is "six billion, six hundred forty-three million, five hundred fifty-four thousand, twenty-one".