21003121021 has 4 divisors (see below), whose sum is σ = 21003626844. Its totient is φ = 21002615200.

The previous prime is 21003121001. The next prime is 21003121049. The reversal of 21003121021 is 12012130012.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 14149102500 + 6854018521 = 118950^2 + 82789^2 .

It is a cyclic number.

It is not a de Polignac number, because 21003121021 - 2⁷ = 21003120893 is a prime.

It is a super-2 number, since 2×21003121021² (a number of 21 digits) contains 22 as substring.

It is a Duffinian number.

It is a junction number, because it is equal to n+sod(n) for n = 21003120992 and 21003121010.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21003121001) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 184450 + ... + 275731.

It is an arithmetic number, because the mean of its divisors is an integer number (5250906711).

Almost surely, 2^21003121021 is an apocalyptic number.

It is an amenable number.

21003121021 is a deficient number, since it is larger than the sum of its proper divisors (505823).

21003121021 is an equidigital number, since it uses as much as digits as its factorization.

21003121021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 505822.

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

Adding to 21003121021 its reverse (12012130012), we get a palindrome (33015251033).

The spelling of 21003121021 in words is "twenty-one billion, three million, one hundred twenty-one thousand, twenty-one".