20018821 has 2 divisors, whose sum is σ = 20018822. Its totient is φ = 20018820.

The previous prime is 20018819. The next prime is 20018833. The reversal of 20018821 is 12881002.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 13793796 + 6225025 = 3714^2 + 2495^2 .

It is a cyclic number.

It is not a de Polignac number, because 20018821 - 2¹ = 20018819 is a prime.

Together with 20018819, it forms a pair of twin primes.

It is a junction number, because it is equal to n+sod(n) for n = 20018792 and 20018801.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (20018881) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10009410 + 10009411.

It is an arithmetic number, because the mean of its divisors is an integer number (10009411).

Almost surely, 2^20018821 is an apocalyptic number.

It is an amenable number.

20018821 is a deficient number, since it is larger than the sum of its proper divisors (1).

20018821 is an equidigital number, since it uses as much as digits as its factorization.

20018821 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 256, while the sum is 22.

The square root of 20018821 is about 4474.2397119511. The cubic root of 20018821 is about 271.5268817209.

Adding to 20018821 its reverse (12881002), we get a palindrome (32899823).

The spelling of 20018821 in words is "twenty million, eighteen thousand, eight hundred twenty-one".