21978544 has 40 divisors (see below), whose sum is σ = 49479968. Its totient is φ = 9262080.

The previous prime is 21978527. The next prime is 21978553. The reversal of 21978544 is 44587912.

It is a junction number, because it is equal to n+sod(n) for n = 21978497 and 21978506.

It is an unprimeable number.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 5224 + ... + 8440.

Almost surely, 2^21978544 is an apocalyptic number.

It is an amenable number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21978544, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (24739984).

21978544 is an abundant number, since it is smaller than the sum of its proper divisors (27501424).

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

21978544 is a wasteful number, since it uses less digits than its factorization.

21978544 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 3293 (or 3287 counting only the distinct ones).

The product of its digits is 80640, while the sum is 40.

The square root of 21978544 is about 4688.1279846011. The cubic root of 21978544 is about 280.1128116851.

It can be divided in two parts, 21978 and 544, that added together give a palindrome (22522).

The spelling of 21978544 in words is "twenty-one million, nine hundred seventy-eight thousand, five hundred forty-four".