21513 has 8 divisors (see below), whose sum is σ = 29376. Its totient is φ = 14000.

The previous prime is 21503. The next prime is 21517. The reversal of 21513 is 31512.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a cyclic number.

It is not a de Polignac number, because 21513 - 2⁵ = 21481 is a prime.

It is an Ulam number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21517) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (5) of ones.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 163 + ... + 263.

It is an arithmetic number, because the mean of its divisors is an integer number (3672).

2²¹⁵¹³ is an apocalyptic number.

It is an amenable number.

21513 is a deficient number, since it is larger than the sum of its proper divisors (7863).

21513 is a wasteful number, since it uses less digits than its factorization.

21513 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 175.

The product of its digits is 30, while the sum is 12.

The square root of 21513 is about 146.6731059193. The cubic root of 21513 is about 27.8120921120.

Subtracting 21513 from its reverse (31512), we obtain a palindrome (9999).

The spelling of 21513 in words is "twenty-one thousand, five hundred thirteen".