21001221101221 has 2 divisors, whose sum is σ = 21001221101222. Its totient is φ = 21001221101220.

The previous prime is 21001221101219. The next prime is 21001221101281. The reversal of 21001221101221 is 12210112210012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18088604424900 + 2912616676321 = 4253070^2 + 1706639^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001221101221 - 2¹ = 21001221101219 is a prime.

Together with 21001221101219, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 21001221101195 and 21001221101204.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21001221101281) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500610550610 + 10500610550611.

It is an arithmetic number, because the mean of its divisors is an integer number (10500610550611).

Almost surely, 2^{21001221101221} is an apocalyptic number.

It is an amenable number.

21001221101221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001221101221 is an equidigital number, since it uses as much as digits as its factorization.

21001221101221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 32, while the sum is 16.

Adding to 21001221101221 its reverse (12210112210012), we get a palindrome (33211333311233).

The spelling of 21001221101221 in words is "twenty-one trillion, one billion, two hundred twenty-one million, one hundred one thousand, two hundred twenty-one".