21653840 has 80 divisors (see below), whose sum is σ = 55496448. Its totient is φ = 7807488.

The previous prime is 21653783. The next prime is 21653893. The reversal of 21653840 is 4835612.

It is a tau number, because it is divible by the number of its divisors (80).

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 48659 + ... + 49101.

Almost surely, 2^21653840 is an apocalyptic number.

21653840 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 21653840, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27748224).

21653840 is an abundant number, since it is smaller than the sum of its proper divisors (33842608).

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

21653840 is a wasteful number, since it uses less digits than its factorization.

21653840 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 516 (or 510 counting only the distinct ones).

The product of its (nonzero) digits is 5760, while the sum is 29.

The square root of 21653840 is about 4653.3686722631. The cubic root of 21653840 is about 278.7265298263.

The spelling of 21653840 in words is "twenty-one million, six hundred fifty-three thousand, eight hundred forty".