20420721 has 8 divisors (see below), whose sum is σ = 30252960. Its totient is φ = 13613796.

The previous prime is 20420681. The next prime is 20420759. The reversal of 20420721 is 12702402.

It is not a de Polignac number, because 20420721 - 2⁹ = 20420209 is a prime.

It is a junction number, because it is equal to n+sod(n) for n = 20420694 and 20420703.

It is not an unprimeable number, because it can be changed into a prime (20420761) 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 in 7 ways as a sum of consecutive naturals, for example, 378135 + ... + 378188.

It is an arithmetic number, because the mean of its divisors is an integer number (3781620).

Almost surely, 2^20420721 is an apocalyptic number.

It is an amenable number.

20420721 is a deficient number, since it is larger than the sum of its proper divisors (9832239).

20420721 is an equidigital number, since it uses as much as digits as its factorization.

20420721 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 756332 (or 756326 counting only the distinct ones).

The product of its (nonzero) digits is 224, while the sum is 18.

The square root of 20420721 is about 4518.9291873186. The cubic root of 20420721 is about 273.3319232857.

The spelling of 20420721 in words is "twenty million, four hundred twenty thousand, seven hundred twenty-one".