721981 has 16 divisors (see below), whose sum is σ = 851200. Its totient is φ = 606528.

The previous prime is 721979. The next prime is 721991. The reversal of 721981 is 189127.

It is not a de Polignac number, because 721981 - 2¹ = 721979 is a prime.

It is a super-2 number, since 2×721981² = 1042513128722, which contains 22 as substring.

721981 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721921) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 9100 + ... + 9178.

It is an arithmetic number, because the mean of its divisors is an integer number (53200).

2⁷²¹⁹⁸¹ is an apocalyptic number.

It is an amenable number.

721981 is a deficient number, since it is larger than the sum of its proper divisors (129219).

721981 is a wasteful number, since it uses less digits than its factorization.

721981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 148.

The product of its digits is 1008, while the sum is 28.

The square root of 721981 is about 849.6946510365. The cubic root of 721981 is about 89.7102202391.

The spelling of 721981 in words is "seven hundred twenty-one thousand, nine hundred eighty-one".