21131544 has 128 divisors (see below), whose sum is σ = 65664000. Its totient is φ = 5644800.

The previous prime is 21131531. The next prime is 21131567. The reversal of 21131544 is 44513112.

It is a Harshad number since it is a multiple of its sum of digits (21).

It is a self number, because there is not a number n which added to its sum of digits gives 21131544.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 31 ways as a sum of consecutive naturals, for example, 139869 + ... + 140019.

It is an arithmetic number, because the mean of its divisors is an integer number (513000).

Almost surely, 2^21131544 is an apocalyptic number.

21131544 is a gapful number since it is divisible by the number (24) formed by its first and last digit.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21131544, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32832000).

21131544 is an abundant number, since it is smaller than the sum of its proper divisors (44532456).

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

21131544 is a wasteful number, since it uses less digits than its factorization.

21131544 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 198 (or 180 counting only the distinct ones).

The product of its digits is 480, while the sum is 21.

The square root of 21131544 is about 4596.9059159395. The cubic root of 21131544 is about 276.4672823542.

Adding to 21131544 its reverse (44513112), we get a palindrome (65644656).

The spelling of 21131544 in words is "twenty-one million, one hundred thirty-one thousand, five hundred forty-four".