20420921 has 2 divisors, whose sum is σ = 20420922. Its totient is φ = 20420920.

The previous prime is 20420891. The next prime is 20420923. The reversal of 20420921 is 12902402.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 13424896 + 6996025 = 3664^2 + 2645^2 .

It is a cyclic number.

It is not a de Polignac number, because 20420921 - 2¹⁰ = 20419897 is a prime.

Together with 20420923, it forms a pair of twin primes.

It is a Chen prime.

It is a junction number, because it is equal to n+sod(n) for n = 20420893 and 20420902.

It is not a weakly prime, because it can be changed into another prime (20420923) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10210460 + 10210461.

It is an arithmetic number, because the mean of its divisors is an integer number (10210461).

Almost surely, 2^20420921 is an apocalyptic number.

It is an amenable number.

20420921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20420921 is an equidigital number, since it uses as much as digits as its factorization.

20420921 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 288, while the sum is 20.

The square root of 20420921 is about 4518.9513164007. The cubic root of 20420921 is about 273.3328156180.

The spelling of 20420921 in words is "twenty million, four hundred twenty thousand, nine hundred twenty-one".