21220240 has 80 divisors (see below), whose sum is σ = 51907392. Its totient is φ = 8059392.

The previous prime is 21220231. The next prime is 21220261. The reversal of 21220240 is 4202212.

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

It is a self number, because there is not a number n which added to its sum of digits gives 21220240.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 198267 + ... + 198373.

Almost surely, 2^21220240 is an apocalyptic number.

21220240 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 21220240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25953696).

21220240 is an abundant number, since it is smaller than the sum of its proper divisors (30687152).

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

21220240 is a wasteful number, since it uses less digits than its factorization.

21220240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 224 (or 218 counting only the distinct ones).

The product of its (nonzero) digits is 64, while the sum is 13.

The square root of 21220240 is about 4606.5431724885. The cubic root of 21220240 is about 276.8535502885.

Adding to 21220240 its reverse (4202212), we get a palindrome (25422452).

The spelling of 21220240 in words is "twenty-one million, two hundred twenty thousand, two hundred forty".