20517221 has 2 divisors, whose sum is σ = 20517222. Its totient is φ = 20517220.

The previous prime is 20517199. The next prime is 20517223. The reversal of 20517221 is 12271502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 20349121 + 168100 = 4511^2 + 410^2 .

It is a cyclic number.

It is not a de Polignac number, because 20517221 - 2⁶ = 20517157 is a prime.

Together with 20517223, it forms a pair of twin primes.

It is a Chen prime.

It is equal to p_1301276 and since 20517221 and 1301276 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 = 20517193 and 20517202.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20517223) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10258610 + 10258611.

It is an arithmetic number, because the mean of its divisors is an integer number (10258611).

Almost surely, 2^20517221 is an apocalyptic number.

It is an amenable number.

20517221 is a deficient number, since it is larger than the sum of its proper divisors (1).

20517221 is an equidigital number, since it uses as much as digits as its factorization.

20517221 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 280, while the sum is 20.

The square root of 20517221 is about 4529.5939111580. The cubic root of 20517221 is about 273.7617985921.

Adding to 20517221 its reverse (12271502), we get a palindrome (32788723).

The spelling of 20517221 in words is "twenty million, five hundred seventeen thousand, two hundred twenty-one".