21357 has 16 divisors (see below), whose sum is σ = 36480. Its totient is φ = 12096.

The previous prime is 21347. The next prime is 21377. The reversal of 21357 is 75312.

It is not a de Polignac number, because 21357 - 2⁴ = 21341 is a prime.

It is a super-2 number, since 2×21357² = 912242898, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21317) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 133 + ... + 245.

It is an arithmetic number, because the mean of its divisors is an integer number (2280).

2²¹³⁵⁷ is an apocalyptic number.

21357 is a gapful number since it is divisible by the number (27) formed by its first and last digit.

It is an amenable number.

21357 is a deficient number, since it is larger than the sum of its proper divisors (15123).

21357 is a wasteful number, since it uses less digits than its factorization.

21357 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 129 (or 123 counting only the distinct ones).

The product of its digits is 210, while the sum is 18.

The square root of 21357 is about 146.1403435058. The cubic root of 21357 is about 27.7447031526.

Adding to 21357 its reverse (75312), we get a palindrome (96669).

It can be divided in two parts, 21 and 357, that added together give a triangular number (378 = T₂₇).

The spelling of 21357 in words is "twenty-one thousand, three hundred fifty-seven".