551721 has 4 divisors (see below), whose sum is σ = 735632. Its totient is φ = 367812.

The previous prime is 551717. The next prime is 551723. The reversal of 551721 is 127155.

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 not a de Polignac number, because 551721 - 2² = 551717 is a prime.

It is a D-number.

It is a Duffinian number.

551721 is a lucky number.

It is an inconsummate number, since it does not exist a number n which divided by its sum of digits gives 551721.

It is not an unprimeable number, because it can be changed into a prime (551723) 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, 91951 + ... + 91956.

It is an arithmetic number, because the mean of its divisors is an integer number (183908).

2⁵⁵¹⁷²¹ is an apocalyptic number.

It is an amenable number.

551721 is a deficient number, since it is larger than the sum of its proper divisors (183911).

551721 is a wasteful number, since it uses less digits than its factorization.

551721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 183910.

The product of its digits is 350, while the sum is 21.

The square root of 551721 is about 742.7792404207. The cubic root of 551721 is about 82.0174957710.

Adding to 551721 its reverse (127155), we get a palindrome (678876).

The spelling of 551721 in words is "five hundred fifty-one thousand, seven hundred twenty-one".