21240040 has 32 divisors (see below), whose sum is σ = 49870080. Its totient is φ = 8126272.

The previous prime is 21240001. The next prime is 21240049. The reversal of 21240040 is 4004212.

It is a super-2 number, since 2×21240040² = 902278598403200, 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 21240040.

It is not an unprimeable number, because it can be changed into a prime (21240049) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 10624 + ... + 12463.

It is an arithmetic number, because the mean of its divisors is an integer number (1558440).

Almost surely, 2^21240040 is an apocalyptic number.

21240040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21240040 is an abundant number, since it is smaller than the sum of its proper divisors (28630040).

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

21240040 is a wasteful number, since it uses less digits than its factorization.

21240040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 23121 (or 23117 counting only the distinct ones).

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

The square root of 21240040 is about 4608.6917883495. The cubic root of 21240040 is about 276.9396315681.

Adding to 21240040 its reverse (4004212), we get a palindrome (25244252).

The spelling of 21240040 in words is "twenty-one million, two hundred forty thousand, forty".