21432780 has 144 divisors (see below), whose sum is σ = 70447104. Its totient is φ = 5258880.

The previous prime is 21432751. The next prime is 21432781. The reversal of 21432780 is 8723412.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21432781) by changing a digit.

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 47 ways as a sum of consecutive naturals, for example, 128257 + ... + 128423.

It is an arithmetic number, because the mean of its divisors is an integer number (489216).

Almost surely, 2^21432780 is an apocalyptic number.

21432780 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 21432780, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (35223552).

21432780 is an abundant number, since it is smaller than the sum of its proper divisors (49014324).

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

21432780 is a wasteful number, since it uses less digits than its factorization.

21432780 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 236 (or 231 counting only the distinct ones).

The product of its (nonzero) digits is 2688, while the sum is 27.

The square root of 21432780 is about 4629.5550542142. Note that the first 3 decimals coincide. The cubic root of 21432780 is about 277.7747947532.

The spelling of 21432780 in words is "twenty-one million, four hundred thirty-two thousand, seven hundred eighty".