21054240 has 72 divisors (see below), whose sum is σ = 71852508. Its totient is φ = 5614080.

The previous prime is 21054233. The next prime is 21054247. The reversal of 21054240 is 4245012.

It is an interprime number because it is at equal distance from previous prime (21054233) and next prime (21054247).

It can be written as a sum of positive squares in 2 ways, for example, as 16941456 + 4112784 = 4116^2 + 2028^2 .

It is a tau number, because it is divible by the number of its divisors (72).

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

It is not an unprimeable number, because it can be changed into a prime (21054247) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (7) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 5871 + ... + 8750.

Almost surely, 2^21054240 is an apocalyptic number.

21054240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21054240 is an abundant number, since it is smaller than the sum of its proper divisors (50798268).

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

21054240 is a wasteful number, since it uses less digits than its factorization.

21054240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 14642 (or 14631 counting only the distinct ones).

The product of its (nonzero) digits is 320, while the sum is 18.

The square root of 21054240 is about 4588.4899476843. The cubic root of 21054240 is about 276.1297436627.

Adding to 21054240 its reverse (4245012), we get a palindrome (25299252).

The spelling of 21054240 in words is "twenty-one million, fifty-four thousand, two hundred forty".