21978750 has 40 divisors (see below), whose sum is σ = 54938664. Its totient is φ = 5860000.

The previous prime is 21978743. The next prime is 21978779. The reversal of 21978750 is 5787912.

It is a junction number, because it is equal to n+sod(n) for n = 21978699 and 21978708.

It is a congruent number.

It is an unprimeable number.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 19 ways as a sum of consecutive naturals, for example, 820 + ... + 6680.

Almost surely, 2^21978750 is an apocalyptic number.

It is a practical number, because each smaller number is the sum of distinct divisors of 21978750, and also a Zumkeller number, because its divisors can be partitioned in two sets with the same sum (27469332).

21978750 is an abundant number, since it is smaller than the sum of its proper divisors (32959914).

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

21978750 is an equidigital number, since it uses as much as digits as its factorization.

21978750 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 5886 (or 5871 counting only the distinct ones).

The product of its (nonzero) digits is 35280, while the sum is 39.

The square root of 21978750 is about 4688.1499549396. The cubic root of 21978750 is about 280.1136868273.

The spelling of 21978750 in words is "twenty-one million, nine hundred seventy-eight thousand, seven hundred fifty".