21201221021 has 2 divisors, whose sum is σ = 21201221022. Its totient is φ = 21201221020.

The previous prime is 21201220981. The next prime is 21201221051. The reversal of 21201221021 is 12012210212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20624980996 + 576240025 = 143614^2 + 24005^2 .

It is a cyclic number.

It is not a de Polignac number, because 21201221021 - 2¹⁰ = 21201219997 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21201220987 and 21201221005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21201221051) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10600610510 + 10600610511.

It is an arithmetic number, because the mean of its divisors is an integer number (10600610511).

Almost surely, 2^21201221021 is an apocalyptic number.

It is an amenable number.

21201221021 is a deficient number, since it is larger than the sum of its proper divisors (1).

21201221021 is an equidigital number, since it uses as much as digits as its factorization.

21201221021 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 32, while the sum is 14.

Adding to 21201221021 its reverse (12012210212), we get a palindrome (33213431233).

It can be divided in two parts, 2 and 1201221021, that multiplied together give a palindrome (2402442042).

The spelling of 21201221021 in words is "twenty-one billion, two hundred one million, two hundred twenty-one thousand, twenty-one".