21783978 has 56 divisors (see below), whose sum is σ = 49945728. Its totient is φ = 7120872.

The previous prime is 21783947. The next prime is 21783989. The reversal of 21783978 is 87938712.

It is an unprimeable number.

It is a polite number, since it can be written in 27 ways as a sum of consecutive naturals, for example, 97575 + ... + 97797.

It is an arithmetic number, because the mean of its divisors is an integer number (891888).

Almost surely, 2^21783978 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21783978, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24972864).

21783978 is an abundant number, since it is smaller than the sum of its proper divisors (28161750).

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

21783978 is an equidigital number, since it uses as much as digits as its factorization.

21783978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 310 (or 295 counting only the distinct ones).

The product of its digits is 169344, while the sum is 45.

The square root of 21783978 is about 4667.3309289143. The cubic root of 21783978 is about 279.2837903235.

The spelling of 21783978 in words is "twenty-one million, seven hundred eighty-three thousand, nine hundred seventy-eight".