21635640 has 256 divisors, whose sum is σ = 82252800. Its totient is φ = 5018112.

The previous prime is 21635609. The next prime is 21635641. The reversal of 21635640 is 4653612.

21635640 = T₂₂₁ + T₂₂₂ + ... + T₅₁₉.

21635640 is a `hidden beast` number, since 2 + 16 + 3 + 5 + 640 = 666.

It is a Harshad number since it is a multiple of its sum of digits (27).

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21635641) by changing a digit.

It is a polite number, since it can be written in 63 ways as a sum of consecutive naturals, for example, 322887 + ... + 322953.

It is an arithmetic number, because the mean of its divisors is an integer number (321300).

Almost surely, 2^21635640 is an apocalyptic number.

21635640 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 21635640, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41126400).

21635640 is an abundant number, since it is smaller than the sum of its proper divisors (60617160).

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

21635640 is a wasteful number, since it uses less digits than its factorization.

21635640 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 123 (or 113 counting only the distinct ones).

The product of its (nonzero) digits is 4320, while the sum is 27.

The square root of 21635640 is about 4651.4126886356. The cubic root of 21635640 is about 278.6484182806.

The spelling of 21635640 in words is "twenty-one million, six hundred thirty-five thousand, six hundred forty".