21256 has 8 divisors (see below), whose sum is σ = 39870. Its totient is φ = 10624.

The previous prime is 21247. The next prime is 21269. The reversal of 21256 is 65212.

It is a happy number.

It can be written as a sum of positive squares in only one way, i.e., 16900 + 4356 = 130^2 + 66^2 .

It is a tau number, because it is divible by the number of its divisors (8).

It is an alternating number because its digits alternate between even and odd.

It is a congruent number.

It is an unprimeable number.

21256 is an untouchable number, because it is not equal to the sum of proper divisors of any number.

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 as a sum of consecutive naturals, namely, 1321 + ... + 1336.

2²¹²⁵⁶ is an apocalyptic number.

It is an amenable number.

21256 is a deficient number, since it is larger than the sum of its proper divisors (18614).

21256 is a wasteful number, since it uses less digits than its factorization.

21256 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 2663 (or 2659 counting only the distinct ones).

The product of its digits is 120, while the sum is 16.

The square root of 21256 is about 145.7943757489. The cubic root of 21256 is about 27.7008979365.

Adding to 21256 its reverse (65212), we get a palindrome (86468).

Subtracting 21256 from its reverse (65212), we obtain a triangular number (43956 = T₂₉₆).

The spelling of 21256 in words is "twenty-one thousand, two hundred fifty-six".