12821721 has 16 divisors (see below), whose sum is σ = 19155648. Its totient is φ = 7560000.

The previous prime is 12821717. The next prime is 12821729. The reversal of 12821721 is 12712821.

12821721 is digitally balanced in base 2 and base 4, because in such bases it contains all the possibile digits an equal number of times.

It is not a de Polignac number, because 12821721 - 2² = 12821717 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 12821691 and 12821700.

It is not an unprimeable number, because it can be changed into a prime (12821729) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 4030 + ... + 6471.

It is an arithmetic number, because the mean of its divisors is an integer number (1197228).

Almost surely, 2^12821721 is an apocalyptic number.

12821721 is a gapful number since it is divisible by the number (11) formed by its first and last digit.

It is an amenable number.

12821721 is a deficient number, since it is larger than the sum of its proper divisors (6333927).

12821721 is a wasteful number, since it uses less digits than its factorization.

12821721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 10552.

The product of its digits is 448, while the sum is 24.

The square root of 12821721 is about 3580.7430793063. The cubic root of 12821721 is about 234.0536621761.

Subtracting from 12821721 its reverse (12712821), we obtain a square (108900 = 330²).

It can be divided in two parts, 1282 and 1721, that added together give a palindrome (3003).

The spelling of 12821721 in words is "twelve million, eight hundred twenty-one thousand, seven hundred twenty-one".