21121240 has 64 divisors (see below), whose sum is σ = 54711360. Its totient is φ = 7188480.

The previous prime is 21121237. The next prime is 21121241. The reversal of 21121240 is 4212112.

It is a happy number.

It is a super-2 number, since 2×21121240² = 892213558275200, 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 21121240.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21121241) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 67324 + ... + 67636.

It is an arithmetic number, because the mean of its divisors is an integer number (854865).

Almost surely, 2^21121240 is an apocalyptic number.

21121240 is a gapful number since it is divisible by the number (20) 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 21121240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27355680).

21121240 is an abundant number, since it is smaller than the sum of its proper divisors (33590120).

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

21121240 is a wasteful number, since it uses less digits than its factorization.

21121240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 572 (or 568 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 13.

The square root of 21121240 is about 4595.7850254336. The cubic root of 21121240 is about 276.4223387693.

Adding to 21121240 its reverse (4212112), we get a palindrome (25333352).

The spelling of 21121240 in words is "twenty-one million, one hundred twenty-one thousand, two hundred forty".