21227821 has 2 divisors, whose sum is σ = 21227822. Its totient is φ = 21227820.

The previous prime is 21227819. The next prime is 21227851. The reversal of 21227821 is 12872212.

21227821 is nontrivially palindromic in base 13.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 15515721 + 5712100 = 3939^2 + 2390^2 .

It is a cyclic number.

It is not a de Polignac number, because 21227821 - 2¹ = 21227819 is a prime.

Together with 21227819, 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 (21227851) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10613910 + 10613911.

It is an arithmetic number, because the mean of its divisors is an integer number (10613911).

Almost surely, 2^21227821 is an apocalyptic number.

It is an amenable number.

21227821 is a deficient number, since it is larger than the sum of its proper divisors (1).

21227821 is an equidigital number, since it uses as much as digits as its factorization.

21227821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 896, while the sum is 25.

The square root of 21227821 is about 4607.3659503018. The cubic root of 21227821 is about 276.8865153080.

The spelling of 21227821 in words is "twenty-one million, two hundred twenty-seven thousand, eight hundred twenty-one".