721505 has 8 divisors (see below), whose sum is σ = 874152. Its totient is φ = 571648.

The previous prime is 721499. The next prime is 721529. The reversal of 721505 is 505127.

It can be written as a sum of positive squares in 4 ways, for example, as 4096 + 717409 = 64^2 + 847^2 .

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 721505 - 2¹⁰ = 720481 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 74 + ... + 1203.

It is an arithmetic number, because the mean of its divisors is an integer number (109269).

It is the magic constant of a 113 × 113 magic square.

2⁷²¹⁵⁰⁵ is an apocalyptic number.

It is an amenable number.

721505 is a deficient number, since it is larger than the sum of its proper divisors (152647).

721505 is a wasteful number, since it uses less digits than its factorization.

721505 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1395.

The product of its (nonzero) digits is 350, while the sum is 20.

The square root of 721505 is about 849.4145042322. The cubic root of 721505 is about 89.6905006746.

It can be divided in two parts, 7 and 21505, that added together give a palindrome (21512).

The spelling of 721505 in words is "seven hundred twenty-one thousand, five hundred five".