21012240 has 80 divisors (see below), whose sum is σ = 67406400. Its totient is φ = 5408256.

The previous prime is 21012239. The next prime is 21012241. The reversal of 21012240 is 4221012.

It is an interprime number because it is at equal distance from previous prime (21012239) and next prime (21012241).

It is a tau number, because it is divible by the number of its divisors (80).

It is a Harshad number since it is a multiple of its sum of digits (12).

It is not an unprimeable number, because it can be changed into a prime (21012241) 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, 5451 + ... + 8469.

It is an arithmetic number, because the mean of its divisors is an integer number (842580).

Almost surely, 2^21012240 is an apocalyptic number.

21012240 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 21012240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (33703200).

21012240 is an abundant number, since it is smaller than the sum of its proper divisors (46394160).

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

21012240 is a wasteful number, since it uses less digits than its factorization.

21012240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3064 (or 3058 counting only the distinct ones).

The product of its (nonzero) digits is 32, while the sum is 12.

The square root of 21012240 is about 4583.9109939003. The cubic root of 21012240 is about 275.9460091828.

Adding to 21012240 its reverse (4221012), we get a palindrome (25233252).

The spelling of 21012240 in words is "twenty-one million, twelve thousand, two hundred forty".