721861 has 4 divisors (see below), whose sum is σ = 824992. Its totient is φ = 618732.

The previous prime is 721859. The next prime is 721883. The reversal of 721861 is 168127.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4.

It is a cyclic number.

It is not a de Polignac number, because 721861 - 2¹ = 721859 is a prime.

721861 is a lucky number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (721891) 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, 51555 + ... + 51568.

It is an arithmetic number, because the mean of its divisors is an integer number (206248).

2⁷²¹⁸⁶¹ is an apocalyptic number.

It is an amenable number.

721861 is a deficient number, since it is larger than the sum of its proper divisors (103131).

721861 is a wasteful number, since it uses less digits than its factorization.

721861 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 103130.

The product of its digits is 672, while the sum is 25.

The square root of 721861 is about 849.6240345000. The cubic root of 721861 is about 89.7052497376.

Adding to 721861 its reverse (168127), we get a palindrome (889988).

The spelling of 721861 in words is "seven hundred twenty-one thousand, eight hundred sixty-one".