20471821 has 2 divisors, whose sum is σ = 20471822. Its totient is φ = 20471820.

The previous prime is 20471819. The next prime is 20471881. The reversal of 20471821 is 12817402.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 17547721 + 2924100 = 4189^2 + 1710^2 .

It is a cyclic number.

It is not a de Polignac number, because 20471821 - 2¹ = 20471819 is a prime.

Together with 20471819, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20471881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10235910 + 10235911.

It is an arithmetic number, because the mean of its divisors is an integer number (10235911).

Almost surely, 2^20471821 is an apocalyptic number.

It is an amenable number.

20471821 is a deficient number, since it is larger than the sum of its proper divisors (1).

20471821 is an equidigital number, since it uses as much as digits as its factorization.

20471821 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 896, while the sum is 25.

The square root of 20471821 is about 4524.5796489840. The cubic root of 20471821 is about 273.5597250216.

The spelling of 20471821 in words is "twenty million, four hundred seventy-one thousand, eight hundred twenty-one".