21780080 has 160 divisors (see below), whose sum is σ = 64281600. Its totient is φ = 6690816.

The previous prime is 21780079. The next prime is 21780097. The reversal of 21780080 is 8008712.

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 31 ways as a sum of consecutive naturals, for example, 244676 + ... + 244764.

It is an arithmetic number, because the mean of its divisors is an integer number (401760).

Almost surely, 2^21780080 is an apocalyptic number.

21780080 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 21780080, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (32140800).

21780080 is an abundant number, since it is smaller than the sum of its proper divisors (42501520).

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

21780080 is a wasteful number, since it uses less digits than its factorization.

21780080 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 151 (or 145 counting only the distinct ones).

The product of its (nonzero) digits is 896, while the sum is 26.

The square root of 21780080 is about 4666.9133268146. The cubic root of 21780080 is about 279.2671310896.

Adding to 21780080 its reverse (8008712), we get a palindrome (29788792).

The spelling of 21780080 in words is "twenty-one million, seven hundred eighty thousand, eighty".