20555921 has 2 divisors, whose sum is σ = 20555922. Its totient is φ = 20555920.

The previous prime is 20555911. The next prime is 20555923. The reversal of 20555921 is 12955502.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19018321 + 1537600 = 4361^2 + 1240^2 .

It is a cyclic number.

It is not a de Polignac number, because 20555921 - 2¹⁴ = 20539537 is a prime.

It is a Sophie Germain prime.

Together with 20555923, it forms a pair of twin primes.

It is a Chen prime.

It is a Curzon number.

It is not a weakly prime, because it can be changed into another prime (20555923) 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, 10277960 + 10277961.

It is an arithmetic number, because the mean of its divisors is an integer number (10277961).

Almost surely, 2^20555921 is an apocalyptic number.

It is an amenable number.

20555921 is a deficient number, since it is larger than the sum of its proper divisors (1).

20555921 is an equidigital number, since it uses as much as digits as its factorization.

20555921 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 4500, while the sum is 29.

The square root of 20555921 is about 4533.8638047476. The cubic root of 20555921 is about 273.9338155097.

The spelling of 20555921 in words is "twenty million, five hundred fifty-five thousand, nine hundred twenty-one".