21221216021 has 2 divisors, whose sum is σ = 21221216022. Its totient is φ = 21221216020.

The previous prime is 21221216011. The next prime is 21221216053. The reversal of 21221216021 is 12061212212.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18896626225 + 2324589796 = 137465^2 + 48214^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21221216021 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21221215984 and 21221216002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21221216011) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610608010 + 10610608011.

It is an arithmetic number, because the mean of its divisors is an integer number (10610608011).

Almost surely, 2^21221216021 is an apocalyptic number.

It is an amenable number.

21221216021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21221216021 is an equidigital number, since it uses as much as digits as its factorization.

21221216021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 192, while the sum is 20.

Adding to 21221216021 its reverse (12061212212), we get a palindrome (33282428233).

The spelling of 21221216021 in words is "twenty-one billion, two hundred twenty-one million, two hundred sixteen thousand, twenty-one".