3155728721 has 4 divisors (see below), whose sum is σ = 3155976192. Its totient is φ = 3155481252.

The previous prime is 3155728691. The next prime is 3155728733. The reversal of 3155728721 is 1278275513.

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 a de Polignac number, because none of the positive numbers 2^k-3155728721 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (3155728021) 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, 103505 + ... + 130478.

It is an arithmetic number, because the mean of its divisors is an integer number (788994048).

Almost surely, 2^3155728721 is an apocalyptic number.

It is an amenable number.

3155728721 is a deficient number, since it is larger than the sum of its proper divisors (247471).

3155728721 is a wasteful number, since it uses less digits than its factorization.

3155728721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 247470.

The product of its digits is 117600, while the sum is 41.

The square root of 3155728721 is about 56175.8731218305. The cubic root of 3155728721 is about 1466.7853179205.

The spelling of 3155728721 in words is "three billion, one hundred fifty-five million, seven hundred twenty-eight thousand, seven hundred twenty-one".