21020420221 has 2 divisors, whose sum is σ = 21020420222. Its totient is φ = 21020420220.

The previous prime is 21020420203. The next prime is 21020420227. The reversal of 21020420221 is 12202402012.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13459248196 + 7561172025 = 116014^2 + 86955^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020420221 - 2⁵ = 21020420189 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 21020420195 and 21020420204.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21020420227) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510210110 + 10510210111.

It is an arithmetic number, because the mean of its divisors is an integer number (10510210111).

Almost surely, 2^21020420221 is an apocalyptic number.

It is an amenable number.

21020420221 is a deficient number, since it is larger than the sum of its proper divisors (1).

21020420221 is an equidigital number, since it uses as much as digits as its factorization.

21020420221 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 128, while the sum is 16.

Adding to 21020420221 its reverse (12202402012), we get a palindrome (33222822233).

The spelling of 21020420221 in words is "twenty-one billion, twenty million, four hundred twenty thousand, two hundred twenty-one".