721644 has 72 divisors (see below), whose sum is σ = 2145024. Its totient is φ = 184800.

The previous prime is 721631. The next prime is 721661. The reversal of 721644 is 446127.

721644 = T₉ + T₁₀ + ... + T₁₆₂.

It is a nude number because it is divisible by every one of its digits.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 10129 + ... + 10199.

It is an arithmetic number, because the mean of its divisors is an integer number (29792).

2⁷²¹⁶⁴⁴ 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 721644, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1072512).

721644 is an abundant number, since it is smaller than the sum of its proper divisors (1423380).

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

721644 is a wasteful number, since it uses less digits than its factorization.

721644 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 107 (or 94 counting only the distinct ones).

The product of its digits is 1344, while the sum is 24.

The square root of 721644 is about 849.4963213575. The cubic root of 721644 is about 89.6962600152.

It can be divided in two parts, 7216 and 44, that added together give a triangular number (7260 = T₁₂₀).

The spelling of 721644 in words is "seven hundred twenty-one thousand, six hundred forty-four".