621821 has 2 divisors, whose sum is σ = 621822. Its totient is φ = 621820.

The previous prime is 621799. The next prime is 621833. The reversal of 621821 is 128126.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 436921 + 184900 = 661^2 + 430^2 .

It is a cyclic number.

It is not a de Polignac number, because 621821 - 2⁶ = 621757 is a prime.

It is a super-2 number, since 2×621821² = 773322712082, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 621793 and 621802.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (621871) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 310910 + 310911.

It is an arithmetic number, because the mean of its divisors is an integer number (310911).

2⁶²¹⁸²¹ is an apocalyptic number.

It is an amenable number.

621821 is a deficient number, since it is larger than the sum of its proper divisors (1).

621821 is an equidigital number, since it uses as much as digits as its factorization.

621821 is an evil number, because the sum of its binary digits is even.

The product of its digits is 192, while the sum is 20.

The square root of 621821 is about 788.5562757343. The cubic root of 621821 is about 85.3535905006.

Adding to 621821 its reverse (128126), we get a palindrome (749947).

The spelling of 621821 in words is "six hundred twenty-one thousand, eight hundred twenty-one".