21663040 has 112 divisors (see below), whose sum is σ = 62179200. Its totient is φ = 7022592.

The previous prime is 21662989. The next prime is 21663041. The reversal of 21663040 is 4036612.

It is a tau number, because it is divible by the number of its divisors (112).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21663041) 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, 42306 + ... + 42814.

Almost surely, 2^21663040 is an apocalyptic number.

21663040 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 21663040, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (31089600).

21663040 is an abundant number, since it is smaller than the sum of its proper divisors (40516160).

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

21663040 is a wasteful number, since it uses less digits than its factorization.

21663040 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 552 (or 542 counting only the distinct ones).

The product of its (nonzero) digits is 864, while the sum is 22.

The square root of 21663040 is about 4654.3570984616. The cubic root of 21663040 is about 278.7659981300.

Adding to 21663040 its reverse (4036612), we get a palindrome (25699652).

The spelling of 21663040 in words is "twenty-one million, six hundred sixty-three thousand, forty".