21028213 has 2 divisors, whose sum is σ = 21028214. Its totient is φ = 21028212.

The previous prime is 21028211. The next prime is 21028229. The reversal of 21028213 is 31282012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 20994724 + 33489 = 4582^2 + 183^2 .

It is a cyclic number.

It is not a de Polignac number, because 21028213 - 2¹ = 21028211 is a prime.

It is a super-3 number, since 3×21028213³ (a number of 23 digits) contains 333 as substring.

Together with 21028211, 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 (21028211) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10514106 + 10514107.

It is an arithmetic number, because the mean of its divisors is an integer number (10514107).

Almost surely, 2^21028213 is an apocalyptic number.

It is an amenable number.

21028213 is a deficient number, since it is larger than the sum of its proper divisors (1).

21028213 is an equidigital number, since it uses as much as digits as its factorization.

21028213 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 192, while the sum is 19.

The square root of 21028213 is about 4585.6529524158. The cubic root of 21028213 is about 276.0159139812.

The spelling of 21028213 in words is "twenty-one million, twenty-eight thousand, two hundred thirteen".