821315221 has 2 divisors, whose sum is σ = 821315222. Its totient is φ = 821315220.

The previous prime is 821315219. The next prime is 821315281. The reversal of 821315221 is 122513128.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 801512721 + 19802500 = 28311^2 + 4450^2 .

It is a cyclic number.

It is not a de Polignac number, because 821315221 - 2¹ = 821315219 is a prime.

Together with 821315219, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (821315281) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 410657610 + 410657611.

It is an arithmetic number, because the mean of its divisors is an integer number (410657611).

Almost surely, 2^821315221 is an apocalyptic number.

It is an amenable number.

821315221 is a deficient number, since it is larger than the sum of its proper divisors (1).

821315221 is an equidigital number, since it uses as much as digits as its factorization.

821315221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 960, while the sum is 25.

The square root of 821315221 is about 28658.5976802774. The cubic root of 821315221 is about 936.4903152978.

Adding to 821315221 its reverse (122513128), we get a palindrome (943828349).

The spelling of 821315221 in words is "eight hundred twenty-one million, three hundred fifteen thousand, two hundred twenty-one".