155721657221 has 4 divisors (see below), whose sum is σ = 167700246252. Its totient is φ = 143743068192.

The previous prime is 155721657209. The next prime is 155721657239. The reversal of 155721657221 is 122756127551.

155721657221 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 41000580196 + 114721077025 = 202486^2 + 338705^2 .

It is a cyclic number.

It is not a de Polignac number, because 155721657221 - 2³⁴ = 138541788037 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (155721657121) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 5989294496 + ... + 5989294521.

It is an arithmetic number, because the mean of its divisors is an integer number (41925061563).

Almost surely, 2^155721657221 is an apocalyptic number.

It is an amenable number.

155721657221 is a deficient number, since it is larger than the sum of its proper divisors (11978589031).

155721657221 is a wasteful number, since it uses less digits than its factorization.

155721657221 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 11978589030.

The product of its digits is 294000, while the sum is 44.

The spelling of 155721657221 in words is "one hundred fifty-five billion, seven hundred twenty-one million, six hundred fifty-seven thousand, two hundred twenty-one".