21665040 has 40 divisors (see below), whose sum is σ = 67162368. Its totient is φ = 5777280.

The previous prime is 21665009. The next prime is 21665041. The reversal of 21665040 is 4056612.

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

It is a Harshad number since it is a multiple of its sum of digits (24).

It is a self number, because there is not a number n which added to its sum of digits gives 21665040.

It is not an unprimeable number, because it can be changed into a prime (21665041) 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, 44896 + ... + 45375.

Almost surely, 2^21665040 is an apocalyptic number.

21665040 is a gapful number since it is divisible by the number (20) formed by its first and last digit.

It is an amenable number.

21665040 is an abundant number, since it is smaller than the sum of its proper divisors (45497328).

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

21665040 is a wasteful number, since it uses less digits than its factorization.

21665040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 90287 (or 90281 counting only the distinct ones).

The product of its (nonzero) digits is 1440, while the sum is 24.

The square root of 21665040 is about 4654.5719459473. The cubic root of 21665040 is about 278.7745767173.

It can be divided in two parts, 216 and 65040, that added together give a palindrome (65256).

The spelling of 21665040 in words is "twenty-one million, six hundred sixty-five thousand, forty".