721306 has 4 divisors (see below), whose sum is σ = 1081962. Its totient is φ = 360652.

The previous prime is 721291. The next prime is 721307. The reversal of 721306 is 603127.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 603127 = 7 ⋅86161.

It can be written as a sum of positive squares in only one way, i.e., 549081 + 172225 = 741^2 + 415^2 .

It is not an unprimeable number, because it can be changed into a prime (721307) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 180325 + ... + 180328.

2⁷²¹³⁰⁶ is an apocalyptic number.

721306 is a deficient number, since it is larger than the sum of its proper divisors (360656).

721306 is a wasteful number, since it uses less digits than its factorization.

721306 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 360655.

The product of its (nonzero) digits is 252, while the sum is 19.

The square root of 721306 is about 849.2973566425. The cubic root of 721306 is about 89.6822540000.

It can be divided in two parts, 72 and 1306, that added together give a triangular number (1378 = T₅₂).

The spelling of 721306 in words is "seven hundred twenty-one thousand, three hundred six".