21240144 has 80 divisors (see below), whose sum is σ = 61821440. Its totient is φ = 7068384.

The previous prime is 21240133. The next prime is 21240161. The reversal of 21240144 is 44104212.

It is a super-2 number, since 2×21240144² = 902287434281472, which contains 22 as substring.

It is a hoax number, since the sum of its digits (18) coincides with the sum of the digits of its distinct prime factors.

It is a Harshad number since it is a multiple of its sum of digits (18).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 34689 + ... + 35295.

It is an arithmetic number, because the mean of its divisors is an integer number (772768).

Almost surely, 2^21240144 is an apocalyptic number.

21240144 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 21240144, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (30910720).

21240144 is an abundant number, since it is smaller than the sum of its proper divisors (40581296).

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

21240144 is an frugal number, since it uses more digits than its factorization.

21240144 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 636 (or 612 counting only the distinct ones).

The product of its (nonzero) digits is 256, while the sum is 18.

The square root of 21240144 is about 4608.7030713640. The cubic root of 21240144 is about 276.9400835709.

Adding to 21240144 its reverse (44104212), we get a palindrome (65344356).

The spelling of 21240144 in words is "twenty-one million, two hundred forty thousand, one hundred forty-four".