155721 has 4 divisors (see below), whose sum is σ = 207632. Its totient is φ = 103812.

The previous prime is 155719. The next prime is 155723. The reversal of 155721 is 127551.

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 an interprime number because it is at equal distance from previous prime (155719) and next prime (155723).

It is not a de Polignac number, because 155721 - 2¹ = 155719 is a prime.

It is a D-number.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (155723) 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, 25951 + ... + 25956.

It is an arithmetic number, because the mean of its divisors is an integer number (51908).

2¹⁵⁵⁷²¹ is an apocalyptic number.

It is an amenable number.

155721 is a deficient number, since it is larger than the sum of its proper divisors (51911).

155721 is an equidigital number, since it uses as much as digits as its factorization.

155721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 51910.

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

The square root of 155721 is about 394.6150022490. The cubic root of 155721 is about 53.8000147409.

The spelling of 155721 in words is "one hundred fifty-five thousand, seven hundred twenty-one".