21501240 has 64 divisors (see below), whose sum is σ = 64864800. Its totient is φ = 5701632.

The previous prime is 21501229. The next prime is 21501241. The reversal of 21501240 is 4210512.

It is a super-4 number, since 4×21501240⁴ (a number of 30 digits) contains 4444 as substring.

It is a Harshad number since it is a multiple of its sum of digits (15).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21501241) 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, 27576 + ... + 28344.

Almost surely, 2^21501240 is an apocalyptic number.

21501240 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 21501240, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32432400).

21501240 is an abundant number, since it is smaller than the sum of its proper divisors (43363560).

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

21501240 is a wasteful number, since it uses less digits than its factorization.

21501240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1016 (or 1012 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 15.

The square root of 21501240 is about 4636.9429584587. The cubic root of 21501240 is about 278.0702339669.

Adding to 21501240 its reverse (4210512), we get a palindrome (25711752).

The spelling of 21501240 in words is "twenty-one million, five hundred one thousand, two hundred forty".