21013 has 2 divisors, whose sum is σ = 21014. Its totient is φ = 21012.

The previous prime is 21011. The next prime is 21017. The reversal of 21013 is 31012.

21013 = 102² + 103².

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 10609 + 10404 = 103^2 + 102^2 .

It is a cyclic number.

It is not a de Polignac number, because 21013 - 2¹ = 21011 is a prime.

Together with 21011, it forms a pair of twin primes.

21013 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 20987 and 21005.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21011) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10506 + 10507.

It is an arithmetic number, because the mean of its divisors is an integer number (10507).

2²¹⁰¹³ is an apocalyptic number.

21013 is the 103-rd centered square number.

It is an amenable number.

21013 is a deficient number, since it is larger than the sum of its proper divisors (1).

21013 is an equidigital number, since it uses as much as digits as its factorization.

21013 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 6, while the sum is 7.

The square root of 21013 is about 144.9586147837. The cubic root of 21013 is about 27.5949336076.

Adding to 21013 its reverse (31012), we get a palindrome (52025).

Subtracting 21013 from its reverse (31012), we obtain a palindrome (9999).

The spelling of 21013 in words is "twenty-one thousand, thirteen".