213121021 has 2 divisors, whose sum is σ = 213121022. Its totient is φ = 213121020.

The previous prime is 213121019. The next prime is 213121057. The reversal of 213121021 is 120121312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 181198521 + 31922500 = 13461^2 + 5650^2 .

It is a cyclic number.

It is not a de Polignac number, because 213121021 - 2¹ = 213121019 is a prime.

Together with 213121019, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 213120992 and 213121010.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (213121421) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 106560510 + 106560511.

It is an arithmetic number, because the mean of its divisors is an integer number (106560511).

Almost surely, 2^213121021 is an apocalyptic number.

It is an amenable number.

213121021 is a deficient number, since it is larger than the sum of its proper divisors (1).

213121021 is an equidigital number, since it uses as much as digits as its factorization.

213121021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 24, while the sum is 13.

The square root of 213121021 is about 14598.6650417084. The cubic root of 213121021 is about 597.3223467685.

Adding to 213121021 its reverse (120121312), we get a palindrome (333242333).

The spelling of 213121021 in words is "two hundred thirteen million, one hundred twenty-one thousand, twenty-one".