21151 has 4 divisors (see below), whose sum is σ = 22792. Its totient is φ = 19512.

The previous prime is 21149. The next prime is 21157. The reversal of 21151 is 15112.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 21151 - 2¹ = 21149 is a prime.

It is a Duffinian number.

It is a nialpdrome in base 13.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21157) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 801 + ... + 826.

It is an arithmetic number, because the mean of its divisors is an integer number (5698).

2²¹¹⁵¹ is an apocalyptic number.

21151 is a deficient number, since it is larger than the sum of its proper divisors (1641).

21151 is a wasteful number, since it uses less digits than its factorization.

21151 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1640.

The product of its digits is 10, while the sum is 10.

The square root of 21151 is about 145.4338337527. The cubic root of 21151 is about 27.6552104954.

Adding to 21151 its reverse (15112), we get a palindrome (36263).

It can be divided in two parts, 2115 and 1, that added together give a square (2116 = 46²).

The spelling of 21151 in words is "twenty-one thousand, one hundred fifty-one".