21011231221 has 2 divisors, whose sum is σ = 21011231222. Its totient is φ = 21011231220.

The previous prime is 21011231183. The next prime is 21011231237. The reversal of 21011231221 is 12213211012.

It is an a-pointer prime, because the next prime (21011231237) can be obtained adding 21011231221 to its sum of digits (16).

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20913498225 + 97732996 = 144615^2 + 9886^2 .

It is a cyclic number.

It is not a de Polignac number, because 21011231221 - 2⁷ = 21011231093 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21011231195 and 21011231204.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21011231261) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10505615610 + 10505615611.

It is an arithmetic number, because the mean of its divisors is an integer number (10505615611).

Almost surely, 2^21011231221 is an apocalyptic number.

It is an amenable number.

21011231221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21011231221 is an equidigital number, since it uses as much as digits as its factorization.

21011231221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48, while the sum is 16.

Adding to 21011231221 its reverse (12213211012), we get a palindrome (33224442233).

The spelling of 21011231221 in words is "twenty-one billion, eleven million, two hundred thirty-one thousand, two hundred twenty-one".