21001201221221 has 16 divisors (see below), whose sum is σ = 22711119050928. Its totient is φ = 19304779161600.

The previous prime is 21001201221211. The next prime is 21001201221391. The reversal of 21001201221221 is 12212210210012.

It can be written as a sum of positive squares in 8 ways, for example, as 377014420225 + 20624186800996 = 614015^2 + 4541386^2 .

It is a cyclic number.

It is not a de Polignac number, because 21001201221221 - 2²² = 21001197026917 is a prime.

It is a Duffinian number.

It is a self number, because there is not a number n which added to its sum of digits gives 21001201221221.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21001201221211) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 175065341 + ... + 175185261.

It is an arithmetic number, because the mean of its divisors is an integer number (1419444940683).

Almost surely, 2^{21001201221221} is an apocalyptic number.

It is an amenable number.

21001201221221 is a deficient number, since it is larger than the sum of its proper divisors (1709917829707).

21001201221221 is a wasteful number, since it uses less digits than its factorization.

21001201221221 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 176072.

The product of its (nonzero) digits is 64, while the sum is 17.

Adding to 21001201221221 its reverse (12212210210012), we get a palindrome (33213411431233).

The spelling of 21001201221221 in words is "twenty-one trillion, one billion, two hundred one million, two hundred twenty-one thousand, two hundred twenty-one".