21009144 has 96 divisors (see below), whose sum is σ = 60343920. Its totient is φ = 6057984.

The previous prime is 21009139. The next prime is 21009151. The reversal of 21009144 is 44190012.

It is a super-2 number, since 2×21009144² = 882768263225472, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 21009144.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 90052 + ... + 90284.

Almost surely, 2^21009144 is an apocalyptic number.

21009144 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 21009144, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30171960).

21009144 is an abundant number, since it is smaller than the sum of its proper divisors (39334776).

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

21009144 is a wasteful number, since it uses less digits than its factorization.

21009144 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 289 (or 268 counting only the distinct ones).

The product of its (nonzero) digits is 288, while the sum is 21.

The square root of 21009144 is about 4583.5732785677. The cubic root of 21009144 is about 275.9324556412.

Adding to 21009144 its reverse (44190012), we get a palindrome (65199156).

The spelling of 21009144 in words is "twenty-one million, nine thousand, one hundred forty-four".