21002001221 has 2 divisors, whose sum is σ = 21002001222. Its totient is φ = 21002001220.

The previous prime is 21002001217. The next prime is 21002001233. The reversal of 21002001221 is 12210020012.

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., 12993720100 + 8008281121 = 113990^2 + 89489^2 .

It is a cyclic number.

It is not a de Polignac number, because 21002001221 - 2² = 21002001217 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21002001271) 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, 10501000610 + 10501000611.

It is an arithmetic number, because the mean of its divisors is an integer number (10501000611).

Almost surely, 2^21002001221 is an apocalyptic number.

It is an amenable number.

21002001221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21002001221 is an equidigital number, since it uses as much as digits as its factorization.

21002001221 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 21002001221 its reverse (12210020012), we get a palindrome (33212021233).

The spelling of 21002001221 in words is "twenty-one billion, two million, one thousand, two hundred twenty-one".