21231231221 has 2 divisors, whose sum is σ = 21231231222. Its totient is φ = 21231231220.

The previous prime is 21231231211. The next prime is 21231231227. The reversal of 21231231221 is 12213213212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13967930596 + 7263300625 = 118186^2 + 85225^2 .

It is a cyclic number.

It is not a de Polignac number, because 21231231221 - 2¹⁸ = 21230969077 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21231231193 and 21231231202.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21231231227) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10615615610 + 10615615611.

It is an arithmetic number, because the mean of its divisors is an integer number (10615615611).

Almost surely, 2^21231231221 is an apocalyptic number.

It is an amenable number.

21231231221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21231231221 is an equidigital number, since it uses as much as digits as its factorization.

21231231221 is an evil number, because the sum of its binary digits is even.

The product of its digits is 288, while the sum is 20.

Adding to 21231231221 its reverse (12213213212), we get a palindrome (33444444433).

The spelling of 21231231221 in words is "twenty-one billion, two hundred thirty-one million, two hundred thirty-one thousand, two hundred twenty-one".