1644664320 has 720 divisors, whose sum is σ = 6859092240. Its totient is φ = 360972288.

The previous prime is 1644664309. The next prime is 1644664331. The reversal of 1644664320 is 234664461.

1644664320 is a `hidden beast` number, since 1 + 6 + 4 + 4 + 6 + 643 + 2 + 0 = 666.

It is an interprime number because it is at equal distance from previous prime (1644664309) and next prime (1644664331).

It is a tau number, because it is divible by the number of its divisors (720).

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

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 71 ways as a sum of consecutive naturals, for example, 86561271 + ... + 86561289.

It is an arithmetic number, because the mean of its divisors is an integer number (9526517).

Almost surely, 2^1644664320 is an apocalyptic number.

1644664320 is a gapful number since it is divisible by the number (10) 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 1644664320, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (3429546120).

1644664320 is an abundant number, since it is smaller than the sum of its proper divisors (5214427920).

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

1644664320 is a wasteful number, since it uses less digits than its factorization.

1644664320 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 95 (or 59 counting only the distinct ones).

The product of its (nonzero) digits is 82944, while the sum is 36.

The square root of 1644664320 is about 40554.4611602719. The cubic root of 1644664320 is about 1180.3906396004.

The spelling of 1644664320 in words is "one billion, six hundred forty-four million, six hundred sixty-four thousand, three hundred twenty".