1221821 has 2 divisors, whose sum is σ = 1221822. Its totient is φ = 1221820.

The previous prime is 1221811. The next prime is 1221823. The reversal of 1221821 is 1281221.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 1125721 + 96100 = 1061^2 + 310^2 .

It is an emirp because it is prime and its reverse (1281221) is a distict prime.

It is a cyclic number.

It is not a de Polignac number, because 1221821 - 2¹⁰ = 1220797 is a prime.

It is a Sophie Germain prime.

Together with 1221823, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a self number, because there is not a number n which added to its sum of digits gives 1221821.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (1221823) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 610910 + 610911.

It is an arithmetic number, because the mean of its divisors is an integer number (610911).

2^1221821 is an apocalyptic number.

It is an amenable number.

1221821 is a deficient number, since it is larger than the sum of its proper divisors (1).

1221821 is an equidigital number, since it uses as much as digits as its factorization.

1221821 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 64, while the sum is 17.

The square root of 1221821 is about 1105.3601223131. The cubic root of 1221821 is about 106.9061103190.

The spelling of 1221821 in words is "one million, two hundred twenty-one thousand, eight hundred twenty-one".