20506021 has 2 divisors, whose sum is σ = 20506022. Its totient is φ = 20506020.

The previous prime is 20506019. The next prime is 20506037. The reversal of 20506021 is 12060502.

It is a happy number.

It is an a-pointer prime, because the next prime (20506037) can be obtained adding 20506021 to its sum of digits (16).

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 11655396 + 8850625 = 3414^2 + 2975^2 .

It is a cyclic number.

It is not a de Polignac number, because 20506021 - 2¹ = 20506019 is a prime.

Together with 20506019, it forms a pair of twin primes.

It is equal to p_1300615 and since 20506021 and 1300615 have the same sum of digits, it is a Honaker prime.

It is a junction number, because it is equal to n+sod(n) for n = 20505986 and 20506004.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20506001) 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 as a sum of consecutive naturals, namely, 10253010 + 10253011.

It is an arithmetic number, because the mean of its divisors is an integer number (10253011).

Almost surely, 2^20506021 is an apocalyptic number.

It is an amenable number.

20506021 is a deficient number, since it is larger than the sum of its proper divisors (1).

20506021 is an equidigital number, since it uses as much as digits as its factorization.

20506021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 120, while the sum is 16.

The square root of 20506021 is about 4528.3574284723. The cubic root of 20506021 is about 273.7119755641.

Adding to 20506021 its reverse (12060502), we get a palindrome (32566523).

The spelling of 20506021 in words is "twenty million, five hundred six thousand, twenty-one".