21020420549 has 2 divisors, whose sum is σ = 21020420550. Its totient is φ = 21020420548.

The previous prime is 21020420539. The next prime is 21020420563. The reversal of 21020420549 is 94502402012.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11610062500 + 9410358049 = 107750^2 + 97007^2 .

It is a cyclic number.

It is not a de Polignac number, because 21020420549 - 2⁸ = 21020420293 is a prime.

It is a super-2 number, since 2×21020420549² (a number of 21 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21020420539) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10510210274 + 10510210275.

It is an arithmetic number, because the mean of its divisors is an integer number (10510210275).

Almost surely, 2^21020420549 is an apocalyptic number.

It is an amenable number.

21020420549 is a deficient number, since it is larger than the sum of its proper divisors (1).

21020420549 is an equidigital number, since it uses as much as digits as its factorization.

21020420549 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5760, while the sum is 29.

The spelling of 21020420549 in words is "twenty-one billion, twenty million, four hundred twenty thousand, five hundred forty-nine".