21731256 has 48 divisors (see below), whose sum is σ = 59398560. Its totient is φ = 7176960.

The previous prime is 21731243. The next prime is 21731257. The reversal of 21731256 is 65213712.

It is a happy number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21731257) by changing a digit.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 6801 + ... + 9471.

It is an arithmetic number, because the mean of its divisors is an integer number (1237470).

Almost surely, 2^21731256 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 21731256, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (29699280).

21731256 is an abundant number, since it is smaller than the sum of its proper divisors (37667304).

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

21731256 is a wasteful number, since it uses less digits than its factorization.

21731256 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2796 (or 2789 counting only the distinct ones).

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

The square root of 21731256 is about 4661.6795256645. The cubic root of 21731256 is about 279.0582989899.

Adding to 21731256 its reverse (65213712), we get a palindrome (86944968).

The spelling of 21731256 in words is "twenty-one million, seven hundred thirty-one thousand, two hundred fifty-six".