721890 has 48 divisors (see below), whose sum is σ = 2024568. Its totient is φ = 177408.

The previous prime is 721883. The next prime is 721891. The reversal of 721890 is 98127.

It can be written as a sum of positive squares in 4 ways, for example, as 233289 + 488601 = 483^2 + 699^2 .

It is a super-2 number, since 2×721890² = 1042250344200, which contains 22 as substring.

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

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (721891) by changing a digit.

721890 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 862 + ... + 1478.

2⁷²¹⁸⁹⁰ is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 721890, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (1012284).

721890 is an abundant number, since it is smaller than the sum of its proper divisors (1302678).

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

721890 is a wasteful number, since it uses less digits than its factorization.

721890 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 643 (or 640 counting only the distinct ones).

The product of its (nonzero) digits is 1008, while the sum is 27.

The square root of 721890 is about 849.6411007008. The cubic root of 721890 is about 89.7064509926.

The spelling of 721890 in words is "seven hundred twenty-one thousand, eight hundred ninety".