20421251 has 2 divisors, whose sum is σ = 20421252. Its totient is φ = 20421250.

The previous prime is 20421241. The next prime is 20421253. The reversal of 20421251 is 15212402.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 20421251 - 2⁶ = 20421187 is a prime.

Together with 20421253, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (20421253) 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, 10210625 + 10210626.

It is an arithmetic number, because the mean of its divisors is an integer number (10210626).

Almost surely, 2^20421251 is an apocalyptic number.

20421251 is a deficient number, since it is larger than the sum of its proper divisors (1).

20421251 is an equidigital number, since it uses as much as digits as its factorization.

20421251 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 160, while the sum is 17.

The square root of 20421251 is about 4518.9878291494. The cubic root of 20421251 is about 273.3342879536.

Adding to 20421251 its reverse (15212402), we get a palindrome (35633653).

The spelling of 20421251 in words is "twenty million, four hundred twenty-one thousand, two hundred fifty-one".