816721664 has 144 divisors (see below), whose sum is σ = 1878599520. Its totient is φ = 350945280.

The previous prime is 816721663. The next prime is 816721673. The reversal of 816721664 is 466127618.

Its product of digits (96768) is a multiple of the sum of its prime divisors (252).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (816721663) 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, 5961404 + ... + 5961540.

It is an arithmetic number, because the mean of its divisors is an integer number (13045830).

Almost surely, 2^816721664 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 816721664, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (939299760).

816721664 is an abundant number, since it is smaller than the sum of its proper divisors (1061877856).

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

816721664 is a wasteful number, since it uses less digits than its factorization.

816721664 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 266 (or 252 counting only the distinct ones).

The product of its digits is 96768, while the sum is 41.

The square root of 816721664 is about 28578.3425691554. The cubic root of 816721664 is about 934.7411425595.

The spelling of 816721664 in words is "eight hundred sixteen million, seven hundred twenty-one thousand, six hundred sixty-four".