644821817770 has 32 divisors (see below), whose sum is σ = 1250004489552. Its totient is φ = 238080018432.

The previous prime is 644821817749. The next prime is 644821817777. The reversal of 644821817770 is 77718128446.

It can be written as a sum of positive squares in 8 ways, for example, as 165765422449 + 479056395321 = 407143^2 + 692139^2 .

It is not an unprimeable number, because it can be changed into a prime (644821817777) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4934394 + ... + 5063386.

Almost surely, 2^644821817770 is an apocalyptic number.

644821817770 is a deficient number, since it is larger than the sum of its proper divisors (605182671782).

644821817770 is a wasteful number, since it uses less digits than its factorization.

644821817770 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 167466.

The product of its (nonzero) digits is 4214784, while the sum is 55.

The spelling of 644821817770 in words is "six hundred forty-four billion, eight hundred twenty-one million, eight hundred seventeen thousand, seven hundred seventy".