21500240 has 40 divisors (see below), whose sum is σ = 52931880. Its totient is φ = 8093696.

The previous prime is 21500231. The next prime is 21500251. The reversal of 21500240 is 4200512.

It can be written as a sum of positive squares in 4 ways, for example, as 633616 + 20866624 = 796^2 + 4568^2 .

It is a tau number, because it is divible by the number of its divisors (40).

It is a congruent number.

It is an unprimeable number.

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 7 ways as a sum of consecutive naturals, for example, 6545 + ... + 9264.

It is an arithmetic number, because the mean of its divisors is an integer number (1323297).

Almost surely, 2^21500240 is an apocalyptic number.

21500240 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21500240 is an abundant number, since it is smaller than the sum of its proper divisors (31431640).

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

21500240 is a wasteful number, since it uses less digits than its factorization.

21500240 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 15839 (or 15833 counting only the distinct ones).

The product of its (nonzero) digits is 80, while the sum is 14.

The square root of 21500240 is about 4636.8351275412. The cubic root of 21500240 is about 278.0659229823.

Adding to 21500240 its reverse (4200512), we get a palindrome (25700752).

The spelling of 21500240 in words is "twenty-one million, five hundred thousand, two hundred forty".