21203120021 has 2 divisors, whose sum is σ = 21203120022. Its totient is φ = 21203120020.

The previous prime is 21203120017. The next prime is 21203120039. The reversal of 21203120021 is 12002130212.

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., 18510963025 + 2692156996 = 136055^2 + 51886^2 .

It is a cyclic number.

It is not a de Polignac number, because 21203120021 - 2² = 21203120017 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21203119978 and 21203120005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21203120041) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10601560010 + 10601560011.

It is an arithmetic number, because the mean of its divisors is an integer number (10601560011).

Almost surely, 2^21203120021 is an apocalyptic number.

It is an amenable number.

21203120021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21203120021 is an equidigital number, since it uses as much as digits as its factorization.

21203120021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 48, while the sum is 14.

Adding to 21203120021 its reverse (12002130212), we get a palindrome (33205250233).

The spelling of 21203120021 in words is "twenty-one billion, two hundred three million, one hundred twenty thousand, twenty-one".