518120021 has 2 divisors, whose sum is σ = 518120022. Its totient is φ = 518120020.

The previous prime is 518120017. The next prime is 518120023. The reversal of 518120021 is 120021815.

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., 517335025 + 784996 = 22745^2 + 886^2 .

It is a cyclic number.

It is not a de Polignac number, because 518120021 - 2² = 518120017 is a prime.

It is a super-2 number, since 2×518120021² = 536896712322080882, which contains 22 as substring.

Together with 518120023, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 518119975 and 518120002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (518120023) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 259060010 + 259060011.

It is an arithmetic number, because the mean of its divisors is an integer number (259060011).

Almost surely, 2^518120021 is an apocalyptic number.

It is an amenable number.

518120021 is a deficient number, since it is larger than the sum of its proper divisors (1).

518120021 is an equidigital number, since it uses as much as digits as its factorization.

518120021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 160, while the sum is 20.

The square root of 518120021 is about 22762.2499107623. The cubic root of 518120021 is about 803.1748943269.

Adding to 518120021 its reverse (120021815), we get a palindrome (638141836).

The spelling of 518120021 in words is "five hundred eighteen million, one hundred twenty thousand, twenty-one".