21204013 has 2 divisors, whose sum is σ = 21204014. Its totient is φ = 21204012.

The previous prime is 21203977. The next prime is 21204037. The reversal of 21204013 is 31040212.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 19954089 + 1249924 = 4467^2 + 1118^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-21204013 is a prime.

It is a super-2 number, since 2×21204013² = 899220334608338, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 21203984 and 21204002.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21234013) 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, 10602006 + 10602007.

It is an arithmetic number, because the mean of its divisors is an integer number (10602007).

Almost surely, 2^21204013 is an apocalyptic number.

It is an amenable number.

21204013 is a deficient number, since it is larger than the sum of its proper divisors (1).

21204013 is an equidigital number, since it uses as much as digits as its factorization.

21204013 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 48, while the sum is 13.

The square root of 21204013 is about 4604.7815366204. The cubic root of 21204013 is about 276.7829628340.

Adding to 21204013 its reverse (31040212), we get a palindrome (52244225).

The spelling of 21204013 in words is "twenty-one million, two hundred four thousand, thirteen".