21663440 has 60 divisors (see below), whose sum is σ = 53561676. Its totient is φ = 8146944.

The previous prime is 21663437. The next prime is 21663497. The reversal of 21663440 is 4436612.

It can be written as a sum of positive squares in 6 ways, for example, as 59536 + 21603904 = 244^2 + 4648^2 .

It is a congruent number.

It is an unprimeable number.

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 11 ways as a sum of consecutive naturals, for example, 22652 + ... + 23588.

Almost surely, 2^21663440 is an apocalyptic number.

21663440 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 21663440, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (26780838).

21663440 is an abundant number, since it is smaller than the sum of its proper divisors (31898236).

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

21663440 is a wasteful number, since it uses less digits than its factorization.

21663440 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 984 (or 961 counting only the distinct ones).

The product of its (nonzero) digits is 3456, while the sum is 26.

The square root of 21663440 is about 4654.4000687521. The cubic root of 21663440 is about 278.7677138897.

The spelling of 21663440 in words is "twenty-one million, six hundred sixty-three thousand, four hundred forty".