20506206221 has 2 divisors, whose sum is σ = 20506206222. Its totient is φ = 20506206220.

The previous prime is 20506206167. The next prime is 20506206223. The reversal of 20506206221 is 12260260502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 17903778025 + 2602428196 = 133805^2 + 51014^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-20506206221 is a prime.

It is a Sophie Germain prime.

Together with 20506206223, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20506206223) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10253103110 + 10253103111.

It is an arithmetic number, because the mean of its divisors is an integer number (10253103111).

Almost surely, 2^20506206221 is an apocalyptic number.

It is an amenable number.

20506206221 is a deficient number, since it is larger than the sum of its proper divisors (1).

20506206221 is an equidigital number, since it uses as much as digits as its factorization.

20506206221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 2880, while the sum is 26.

Adding to 20506206221 its reverse (12260260502), we get a palindrome (32766466723).

The spelling of 20506206221 in words is "twenty billion, five hundred six million, two hundred six thousand, two hundred twenty-one".