21317256 has 80 divisors (see below), whose sum is σ = 60722640. Its totient is φ = 6985440.

The previous prime is 21317249. The next prime is 21317267. The reversal of 21317256 is 65271312.

It is a happy number.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is an unprimeable number.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 43171 + ... + 43661.

It is an arithmetic number, because the mean of its divisors is an integer number (759033).

Almost surely, 2^21317256 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21317256, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30361320).

21317256 is an abundant number, since it is smaller than the sum of its proper divisors (39405384).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

21317256 is a wasteful number, since it uses less digits than its factorization.

21317256 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 576 (or 563 counting only the distinct ones).

The product of its digits is 2520, while the sum is 27.

The square root of 21317256 is about 4617.0614031005. The cubic root of 21317256 is about 277.2748209789.

Adding to 21317256 its reverse (65271312), we get a palindrome (86588568).

The spelling of 21317256 in words is "twenty-one million, three hundred seventeen thousand, two hundred fifty-six".