644404423656566 has 256 divisors, whose sum is σ = 1130124213504000. Its totient is φ = 273820306636800.

The previous prime is 644404423656443. The next prime is 644404423656607. The reversal of 644404423656566 is 665656324404446.

It is a super-2 number, since 2×644404423656566² (a number of 30 digits) contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 127 ways as a sum of consecutive naturals, for example, 357803676866 + ... + 357803678666.

It is an arithmetic number, because the mean of its divisors is an integer number (4414547709000).

Almost surely, 2^{644404423656566} is an apocalyptic number.

644404423656566 is a deficient number, since it is larger than the sum of its proper divisors (485719789847434).

644404423656566 is a wasteful number, since it uses less digits than its factorization.

644404423656566 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3559.

The product of its (nonzero) digits is 1194393600, while the sum is 65.

The spelling of 644404423656566 in words is "six hundred forty-four trillion, four hundred four billion, four hundred twenty-three million, six hundred fifty-six thousand, five hundred sixty-six".