621553021 has 2 divisors, whose sum is σ = 621553022. Its totient is φ = 621553020.

The previous prime is 621553019. The next prime is 621553087. The reversal of 621553021 is 120355126.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 523265625 + 98287396 = 22875^2 + 9914^2 .

It is a cyclic number.

It is not a de Polignac number, because 621553021 - 2¹ = 621553019 is a prime.

Together with 621553019, 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 (621557021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 310776510 + 310776511.

It is an arithmetic number, because the mean of its divisors is an integer number (310776511).

Almost surely, 2^621553021 is an apocalyptic number.

It is an amenable number.

621553021 is a deficient number, since it is larger than the sum of its proper divisors (1).

621553021 is an equidigital number, since it uses as much as digits as its factorization.

621553021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 1800, while the sum is 25.

The square root of 621553021 is about 24930.9651036618. The cubic root of 621553021 is about 853.4132745576.

The spelling of 621553021 in words is "six hundred twenty-one million, five hundred fifty-three thousand, twenty-one".