721690 has 8 divisors (see below), whose sum is σ = 1299060. Its totient is φ = 288672.

The previous prime is 721687. The next prime is 721697. The reversal of 721690 is 96127.

It can be written as a sum of positive squares in 2 ways, for example, as 641601 + 80089 = 801^2 + 283^2 .

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

It is a super-2 number, since 2×721690² = 1041672912200, which contains 22 as substring.

It is an alternating number because its digits alternate between odd and even.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721697) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 36075 + ... + 36094.

2⁷²¹⁶⁹⁰ is an apocalyptic number.

721690 is a deficient number, since it is larger than the sum of its proper divisors (577370).

721690 is a wasteful number, since it uses less digits than its factorization.

721690 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 72176.

The product of its (nonzero) digits is 756, while the sum is 25.

The square root of 721690 is about 849.5233957932. The cubic root of 721690 is about 89.6981658211.

The spelling of 721690 in words is "seven hundred twenty-one thousand, six hundred ninety".