21613 has 2 divisors, whose sum is σ = 21614. Its totient is φ = 21612.

The previous prime is 21611. The next prime is 21617. The reversal of 21613 is 31612.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 21609 + 4 = 147^2 + 2^2 .

21613 is a truncatable prime.

It is a cyclic number.

It is not a de Polignac number, because 21613 - 2¹ = 21611 is a prime.

Together with 21611, it forms a pair of twin primes.

21613 is a lucky number.

It is a junction number, because it is equal to n+sod(n) for n = 21593 and 21602.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (21611) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10806 + 10807.

It is an arithmetic number, because the mean of its divisors is an integer number (10807).

2²¹⁶¹³ is an apocalyptic number.

It is an amenable number.

21613 is a deficient number, since it is larger than the sum of its proper divisors (1).

21613 is an equidigital number, since it uses as much as digits as its factorization.

21613 is an evil number, because the sum of its binary digits is even.

The product of its digits is 36, while the sum is 13.

The square root of 21613 is about 147.0136048126. The cubic root of 21613 is about 27.8551189789.

Subtracting 21613 from its reverse (31612), we obtain a palindrome (9999).

The spelling of 21613 in words is "twenty-one thousand, six hundred thirteen".