21370021 has 2 divisors, whose sum is σ = 21370022. Its totient is φ = 21370020.

The previous prime is 21370009. The next prime is 21370031. The reversal of 21370021 is 12007312.

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., 12602500 + 8767521 = 3550^2 + 2961^2 .

It is a cyclic number.

It is not a de Polignac number, because 21370021 - 2⁵ = 21369989 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21369977 and 21370004.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21370001) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10685010 + 10685011.

It is an arithmetic number, because the mean of its divisors is an integer number (10685011).

Almost surely, 2^21370021 is an apocalyptic number.

It is an amenable number.

21370021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21370021 is an equidigital number, since it uses as much as digits as its factorization.

21370021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 84, while the sum is 16.

The square root of 21370021 is about 4622.7720038955. The cubic root of 21370021 is about 277.5034049849.

Adding to 21370021 its reverse (12007312), we get a palindrome (33377333).

The spelling of 21370021 in words is "twenty-one million, three hundred seventy thousand, twenty-one".