21252540 has 24 divisors (see below), whose sum is σ = 59507280. Its totient is φ = 5667328.

The previous prime is 21252509. The next prime is 21252547. The reversal of 21252540 is 4525212.

It is a happy number.

It is a super-3 number, since 3×21252540³ (a number of 23 digits) contains 333 as substring.

It is a plaindrome in base 16.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21252547) by changing a digit.

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 7 ways as a sum of consecutive naturals, for example, 177045 + ... + 177164.

It is an arithmetic number, because the mean of its divisors is an integer number (2479470).

Almost surely, 2^21252540 is an apocalyptic number.

21252540 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21252540 is an abundant number, since it is smaller than the sum of its proper divisors (38254740).

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

21252540 is a wasteful number, since it uses less digits than its factorization.

21252540 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 354221 (or 354219 counting only the distinct ones).

The product of its (nonzero) digits is 800, while the sum is 21.

The square root of 21252540 is about 4610.0477220957. The cubic root of 21252540 is about 276.9939482663.

Adding to 21252540 its reverse (4525212), we get a palindrome (25777752).

The spelling of 21252540 in words is "twenty-one million, two hundred fifty-two thousand, five hundred forty".