21220100021 has 2 divisors, whose sum is σ = 21220100022. Its totient is φ = 21220100020.

The previous prime is 21220099991. The next prime is 21220100039. The reversal of 21220100021 is 12000102212.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21173451121 + 46648900 = 145511^2 + 6830^2 .

It is a cyclic number.

It is not a de Polignac number, because 21220100021 - 2²⁶ = 21152991157 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21220099975 and 21220100011.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21220100051) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10610050010 + 10610050011.

It is an arithmetic number, because the mean of its divisors is an integer number (10610050011).

Almost surely, 2^21220100021 is an apocalyptic number.

It is an amenable number.

21220100021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21220100021 is an equidigital number, since it uses as much as digits as its factorization.

21220100021 is an odious number, because the sum of its binary digits is odd.

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

Adding to 21220100021 its reverse (12000102212), we get a palindrome (33220202233).

The spelling of 21220100021 in words is "twenty-one billion, two hundred twenty million, one hundred thousand, twenty-one".