21780808 has 64 divisors (see below), whose sum is σ = 50077440. Its totient is φ = 8669184.

The previous prime is 21780779. The next prime is 21780809. The reversal of 21780808 is 80808712.

It is a Harshad number since it is a multiple of its sum of digits (34).

It is not an unprimeable number, because it can be changed into a prime (21780809) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 130341 + ... + 130507.

It is an arithmetic number, because the mean of its divisors is an integer number (782460).

Almost surely, 2^21780808 is an apocalyptic number.

21780808 is a gapful number since it is divisible by the number (28) 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 21780808, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (25038720).

21780808 is an abundant number, since it is smaller than the sum of its proper divisors (28296632).

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

21780808 is a wasteful number, since it uses less digits than its factorization.

21780808 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 334 (or 330 counting only the distinct ones).

The product of its (nonzero) digits is 7168, while the sum is 34.

The square root of 21780808 is about 4666.9913220404. The cubic root of 21780808 is about 279.2702425598.

The spelling of 21780808 in words is "twenty-one million, seven hundred eighty thousand, eight hundred eight".