1644005664 has 216 divisors, whose sum is σ = 5499070668. Its totient is φ = 464486400.

The previous prime is 1644005663. The next prime is 1644005717. The reversal of 1644005664 is 4665004461.

1644005664 is a `hidden beast` number, since 1 + 644 + 0 + 0 + 5 + 6 + 6 + 4 = 666.

It can be written as a sum of positive squares in 2 ways, for example, as 1397264400 + 246741264 = 37380^2 + 15708^2 .

It is a super-3 number, since 3×1644005664³ (a number of 29 digits) contains 333 as substring.

It is a Harshad number since it is a multiple of its sum of digits (36).

It is not an unprimeable number, because it can be changed into a prime (1644005663) by changing a digit.

It is a polite number, since it can be written in 35 ways as a sum of consecutive naturals, for example, 1368264 + ... + 1369464.

Almost surely, 2^1644005664 is an apocalyptic number.

1644005664 is a gapful number since it is divisible by the number (14) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 1644005664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (2749535334).

1644005664 is an abundant number, since it is smaller than the sum of its proper divisors (3855065004).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

1644005664 is a wasteful number, since it uses less digits than its factorization.

1644005664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1328 (or 1310 counting only the distinct ones).

The product of its (nonzero) digits is 69120, while the sum is 36.

The square root of 1644005664 is about 40546.3397114955. The cubic root of 1644005664 is about 1180.2330440801.

The spelling of 1644005664 in words is "one billion, six hundred forty-four million, five thousand, six hundred sixty-four".