21021212221 has 2 divisors, whose sum is σ = 21021212222. Its totient is φ = 21021212220.

The previous prime is 21021212141. The next prime is 21021212231. The reversal of 21021212221 is 12221212012.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15978224025 + 5042988196 = 126405^2 + 71014^2 .

It is a cyclic number.

It is not a de Polignac number, because 21021212221 - 2³³ = 12431277629 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21021212195 and 21021212204.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21021212231) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510606110 + 10510606111.

It is an arithmetic number, because the mean of its divisors is an integer number (10510606111).

Almost surely, 2^21021212221 is an apocalyptic number.

It is an amenable number.

21021212221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21021212221 is an equidigital number, since it uses as much as digits as its factorization.

21021212221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 64, while the sum is 16.

Adding to 21021212221 its reverse (12221212012), we get a palindrome (33242424233).

The spelling of 21021212221 in words is "twenty-one billion, twenty-one million, two hundred twelve thousand, two hundred twenty-one".