6640449686649 has 21 divisors (see below), whose sum is σ = 9956224355839. Its totient is φ = 4426920073440.

The previous prime is 6640449686623. The next prime is 6640449686659. The reversal of 6640449686649 is 9466869440466.

The square root of 6640449686649 is 2576907.

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

6640449686649 is a `hidden beast` number, since 6 + 6 + 40 + 449 + 6 + 86 + 64 + 9 = 666.

It can be written as a sum of positive squares in only one way, i.e., 5825257392249 + 815192294400 = 2413557^2 + 902880^2 .

It is not a de Polignac number, because 6640449686649 - 2⁹ = 6640449686137 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (6640449686659) by changing a digit.

It is a polite number, since it can be written in 20 ways as a sum of consecutive naturals, for example, 69528769 + ... + 69624209.

Almost surely, 2^{6640449686649} is an apocalyptic number.

6640449686649 is the 2576907-th square number.

6640449686649 is the 1288454-th centered octagonal number.

It is an amenable number.

6640449686649 is a deficient number, since it is larger than the sum of its proper divisors (3315774669190).

6640449686649 is an frugal number, since it uses more digits than its factorization.

6640449686649 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 190900 (or 95444 counting only the distinct ones).

The product of its (nonzero) digits is 1289945088, while the sum is 72.

The spelling of 6640449686649 in words is "six trillion, six hundred forty billion, four hundred forty-nine million, six hundred eighty-six thousand, six hundred forty-nine".