21351 has 8 divisors (see below), whose sum is σ = 31104. Its totient is φ = 12920.

The previous prime is 21347. The next prime is 21377. The reversal of 21351 is 15312.

21351 = 20² + 21² + ... + 41².

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 21351 - 2² = 21347 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21341) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 291 + ... + 356.

It is an arithmetic number, because the mean of its divisors is an integer number (3888).

2²¹³⁵¹ is an apocalyptic number.

21351 is a deficient number, since it is larger than the sum of its proper divisors (9753).

21351 is a wasteful number, since it uses less digits than its factorization.

21351 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 661.

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

The square root of 21351 is about 146.1198138515. The cubic root of 21351 is about 27.7421047257.

Subtracting from 21351 its product of digits (30), we obtain a triangular number (21321 = T₂₀₆).

Adding to 21351 its reverse (15312), we get a palindrome (36663).

The spelling of 21351 in words is "twenty-one thousand, three hundred fifty-one".