21651260221 has 2 divisors, whose sum is σ = 21651260222. Its totient is φ = 21651260220.

The previous prime is 21651260207. The next prime is 21651260237. The reversal of 21651260221 is 12206215612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 18026016121 + 3625244100 = 134261^2 + 60210^2 .

It is a cyclic number.

It is not a de Polignac number, because 21651260221 - 2⁷ = 21651260093 is a prime.

It is a self number, because there is not a number n which added to its sum of digits gives 21651260221.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21651260261) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10825630110 + 10825630111.

It is an arithmetic number, because the mean of its divisors is an integer number (10825630111).

Almost surely, 2^21651260221 is an apocalyptic number.

It is an amenable number.

21651260221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21651260221 is an equidigital number, since it uses as much as digits as its factorization.

21651260221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 2880, while the sum is 28.

Adding to 21651260221 its reverse (12206215612), we get a palindrome (33857475833).

The spelling of 21651260221 in words is "twenty-one billion, six hundred fifty-one million, two hundred sixty thousand, two hundred twenty-one".