21200021 has 2 divisors, whose sum is σ = 21200022.
Its totient is φ = 21200020.
The previous prime is 21199999. The next prime is 21200041. The reversal of 21200021 is 12000212.
Adding to 21200021 its reverse (12000212), we get a palindrome (33200233).
It can be divided in two parts, 2 and 1200021, that multiplied together give a palindrome (2400042).
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 15319396 + 5880625 = 3914^2 + 2425^2
It is a cyclic number.
It is not a de Polignac number, because 21200021 - 210 = 21198997 is a prime.
It is a Chen prime.
It is a junction number, because it is equal to n+sod(n) for n = 21199981 and 21200008.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (21200041) 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, 10600010 + 10600011.
It is an arithmetic number, because the mean of its divisors is an integer number (10600011).
Almost surely, 221200021 is an apocalyptic number.
It is an amenable number.
21200021 is a deficient number, since it is larger than the sum of its proper divisors (1).
21200021 is an equidigital number, since it uses as much as digits as its factorization.
21200021 is an odious number, because the sum of its binary digits is odd.
The product of its (nonzero) digits is 8, while the sum is 8.
The square root of 21200021 is about 4604.3480537422.
The cubic root of 21200021 is about 276.7655921137.
The spelling of 21200021 in words is "twenty-one million, two hundred thousand, twenty-one".