721605 has 16 divisors (see below), whose sum is σ = 1172160. Its totient is φ = 379008.

The previous prime is 721597. The next prime is 721613. The reversal of 721605 is 506127.

It is an interprime number because it is at equal distance from previous prime (721597) and next prime (721613).

It is not a de Polignac number, because 721605 - 2³ = 721597 is a prime.

It is a congruent number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 721605.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 766 + ... + 1424.

It is an arithmetic number, because the mean of its divisors is an integer number (73260).

2⁷²¹⁶⁰⁵ is an apocalyptic number.

It is an amenable number.

721605 is a deficient number, since it is larger than the sum of its proper divisors (450555).

721605 is a wasteful number, since it uses less digits than its factorization.

721605 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 740.

The product of its (nonzero) digits is 420, while the sum is 21.

The square root of 721605 is about 849.4733662688. The cubic root of 721605 is about 89.6946441597.

It can be divided in two parts, 721 and 605, that added together give a triangular number (1326 = T₅₁).

The spelling of 721605 in words is "seven hundred twenty-one thousand, six hundred five".