21978742 has 8 divisors (see below), whose sum is σ = 32993856. Its totient is φ = 10980792.

The previous prime is 21978701. The next prime is 21978743. The reversal of 21978742 is 24787912.

It is a sphenic number, since it is the product of 3 distinct primes.

It is a junction number, because it is equal to n+sod(n) for n = 21978695 and 21978704.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21978743) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 373 + ... + 6640.

It is an arithmetic number, because the mean of its divisors is an integer number (4124232).

Almost surely, 2^21978742 is an apocalyptic number.

21978742 is a deficient number, since it is larger than the sum of its proper divisors (11015114).

21978742 is a wasteful number, since it uses less digits than its factorization.

21978742 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 8582.

The product of its digits is 56448, while the sum is 40.

The square root of 21978742 is about 4688.1491017245. The cubic root of 21978742 is about 280.1136528413.

It can be divided in two parts, 219 and 78742, that added together give a square (78961 = 281²).

The spelling of 21978742 in words is "twenty-one million, nine hundred seventy-eight thousand, seven hundred forty-two".