21331021 has 2 divisors, whose sum is σ = 21331022. Its totient is φ = 21331020.

The previous prime is 21331001. The next prime is 21331043. The reversal of 21331021 is 12013312.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21288996 + 42025 = 4614^2 + 205^2 .

It is a cyclic number.

It is not a de Polignac number, because 21331021 - 2¹⁷ = 21199949 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21330992 and 21331010.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21331001) 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, 10665510 + 10665511.

It is an arithmetic number, because the mean of its divisors is an integer number (10665511).

Almost surely, 2^21331021 is an apocalyptic number.

It is an amenable number.

21331021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21331021 is an equidigital number, since it uses as much as digits as its factorization.

21331021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 36, while the sum is 13.

The square root of 21331021 is about 4618.5518293075. The cubic root of 21331021 is about 277.3344888633.

Adding to 21331021 its reverse (12013312), we get a palindrome (33344333).

The spelling of 21331021 in words is "twenty-one million, three hundred thirty-one thousand, twenty-one".