21012002021 has 2 divisors, whose sum is σ = 21012002022. Its totient is φ = 21012002020.

The previous prime is 21012002009. The next prime is 21012002041. The reversal of 21012002021 is 12020021012.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13493377921 + 7518624100 = 116161^2 + 86710^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21012002021 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21012001993 and 21012002011.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21012002041) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506001010 + 10506001011.

It is an arithmetic number, because the mean of its divisors is an integer number (10506001011).

Almost surely, 2^21012002021 is an apocalyptic number.

It is an amenable number.

21012002021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21012002021 is an equidigital number, since it uses as much as digits as its factorization.

21012002021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 16, while the sum is 11.

Adding to 21012002021 its reverse (12020021012), we get a palindrome (33032023033).

The spelling of 21012002021 in words is "twenty-one billion, twelve million, two thousand, twenty-one".