21784140 has 240 divisors, whose sum is σ = 83426112. Its totient is φ = 4644864.

The previous prime is 21784129. The next prime is 21784177. The reversal of 21784140 is 4148712.

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

It is a zygodrome in base 9.

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 79 ways as a sum of consecutive naturals, for example, 192724 + ... + 192836.

Almost surely, 2^21784140 is an apocalyptic number.

21784140 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 21784140, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (41713056).

21784140 is an abundant number, since it is smaller than the sum of its proper divisors (61641972).

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

21784140 is a wasteful number, since it uses less digits than its factorization.

21784140 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 158 (or 147 counting only the distinct ones).

The product of its (nonzero) digits is 1792, while the sum is 27.

The square root of 21784140 is about 4667.3482835546. The cubic root of 21784140 is about 279.2844826345.

The spelling of 21784140 in words is "twenty-one million, seven hundred eighty-four thousand, one hundred forty".