155005721 has 4 divisors (see below), whose sum is σ = 166929252. Its totient is φ = 143082192.

The previous prime is 155005699. The next prime is 155005727. The reversal of 155005721 is 127500551.

It is a happy number.

155005721 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 59845696 + 95160025 = 7736^2 + 9755^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-155005721 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (155005727) 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, 5961746 + ... + 5961771.

It is an arithmetic number, because the mean of its divisors is an integer number (41732313).

Almost surely, 2^155005721 is an apocalyptic number.

It is an amenable number.

155005721 is a deficient number, since it is larger than the sum of its proper divisors (11923531).

155005721 is a wasteful number, since it uses less digits than its factorization.

155005721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 11923530.

The product of its (nonzero) digits is 1750, while the sum is 26.

The square root of 155005721 is about 12450.1293567577. The cubic root of 155005721 is about 537.1751443190.

The spelling of 155005721 in words is "one hundred fifty-five million, five thousand, seven hundred twenty-one".