20505135221 has 2 divisors, whose sum is σ = 20505135222. Its totient is φ = 20505135220.

The previous prime is 20505135109. The next prime is 20505135223. The reversal of 20505135221 is 12253150502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 15347740996 + 5157394225 = 123886^2 + 71815^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20505135221 is a prime.

Together with 20505135223, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20505135223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10252567610 + 10252567611.

It is an arithmetic number, because the mean of its divisors is an integer number (10252567611).

Almost surely, 2^20505135221 is an apocalyptic number.

It is an amenable number.

20505135221 is a deficient number, since it is larger than the sum of its proper divisors (1).

20505135221 is an equidigital number, since it uses as much as digits as its factorization.

20505135221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3000, while the sum is 26.

Adding to 20505135221 its reverse (12253150502), we get a palindrome (32758285723).

The spelling of 20505135221 in words is "twenty billion, five hundred five million, one hundred thirty-five thousand, two hundred twenty-one".