8129721 has 4 divisors (see below), whose sum is σ = 10839632. Its totient is φ = 5419812.

The previous prime is 8129707. The next prime is 8129743. The reversal of 8129721 is 1279218.

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 8129721 - 2¹⁴ = 8113337 is a prime.

It is a Duffinian number.

8129721 is a lucky number.

It is not an unprimeable number, because it can be changed into a prime (8129761) 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, 1354951 + ... + 1354956.

It is an arithmetic number, because the mean of its divisors is an integer number (2709908).

Almost surely, 2^8129721 is an apocalyptic number.

It is an amenable number.

8129721 is a deficient number, since it is larger than the sum of its proper divisors (2709911).

8129721 is a wasteful number, since it uses less digits than its factorization.

8129721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2709910.

The product of its digits is 2016, while the sum is 30.

The square root of 8129721 is about 2851.2665606709. The cubic root of 8129721 is about 201.0752175111.

It can be divided in two parts, 81297 and 21, that added together give a palindrome (81318).

The spelling of 8129721 in words is "eight million, one hundred twenty-nine thousand, seven hundred twenty-one".