7821221 has 2 divisors, whose sum is σ = 7821222. Its totient is φ = 7821220.

The previous prime is 7821211. The next prime is 7821239. The reversal of 7821221 is 1221287.

7821221 is digitally balanced in base 3, because in such base it contains all the possibile digits an equal number of times.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 4264225 + 3556996 = 2065^2 + 1886^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-7821221 is a prime.

It is a super-2 number, since 2×7821221² = 122342995861682, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (7821211) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3910610 + 3910611.

It is an arithmetic number, because the mean of its divisors is an integer number (3910611).

Almost surely, 2^7821221 is an apocalyptic number.

It is an amenable number.

7821221 is a deficient number, since it is larger than the sum of its proper divisors (1).

7821221 is an equidigital number, since it uses as much as digits as its factorization.

7821221 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 448, while the sum is 23.

The square root of 7821221 is about 2796.6445966551. The cubic root of 7821221 is about 198.4989372377.

The spelling of 7821221 in words is "seven million, eight hundred twenty-one thousand, two hundred twenty-one".