21001221121 has 2 divisors, whose sum is σ = 21001221122. Its totient is φ = 21001221120.

The previous prime is 21001221119. The next prime is 21001221181. The reversal of 21001221121 is 12112210012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13540580496 + 7460640625 = 116364^2 + 86375^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001221121 - 2¹ = 21001221119 is a prime.

Together with 21001221119, it forms a pair of twin primes.

It is not a weakly prime, because it can be changed into another prime (21001221181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10500610560 + 10500610561.

It is an arithmetic number, because the mean of its divisors is an integer number (10500610561).

Almost surely, 2^21001221121 is an apocalyptic number.

It is an amenable number.

21001221121 is a deficient number, since it is larger than the sum of its proper divisors (1).

21001221121 is an equidigital number, since it uses as much as digits as its factorization.

21001221121 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 13.

Adding to 21001221121 its reverse (12112210012), we get a palindrome (33113431133).

It can be divided in two parts, 2100 and 1221121, that added together give a palindrome (1223221).

The spelling of 21001221121 in words is "twenty-one billion, one million, two hundred twenty-one thousand, one hundred twenty-one".