2006521721 has 4 divisors (see below), whose sum is σ = 2013370212. Its totient is φ = 1999673232.

The previous prime is 2006521703. The next prime is 2006521787. The reversal of 2006521721 is 1271256002.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1271256002 = 2 ⋅635628001.

It can be written as a sum of positive squares in 2 ways, for example, as 1862785600 + 143736121 = 43160^2 + 11989^2 .

It is a cyclic number.

It is not a de Polignac number, because 2006521721 - 2¹⁰ = 2006520697 is a prime.

It is a super-2 number, since 2×2006521721² = 8052258833689603682, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (2006521021) 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, 3423806 + ... + 3424391.

It is an arithmetic number, because the mean of its divisors is an integer number (503342553).

Almost surely, 2^2006521721 is an apocalyptic number.

It is an amenable number.

2006521721 is a deficient number, since it is larger than the sum of its proper divisors (6848491).

2006521721 is an equidigital number, since it uses as much as digits as its factorization.

2006521721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 6848490.

The product of its (nonzero) digits is 1680, while the sum is 26.

The square root of 2006521721 is about 44794.2152626877. The cubic root of 2006521721 is about 1261.2890396243.

Adding to 2006521721 its reverse (1271256002), we get a palindrome (3277777723).

The spelling of 2006521721 in words is "two billion, six million, five hundred twenty-one thousand, seven hundred twenty-one".