21981438 has 48 divisors (see below), whose sum is σ = 48977136. Its totient is φ = 7123200.

The previous prime is 21981437. The next prime is 21981451. The reversal of 21981438 is 83418912.

21981438 is a `hidden beast` number, since 219 + 8 + 1 + 438 = 666.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21981433) by changing a digit.

It is a polite number, since it can be written in 23 ways as a sum of consecutive naturals, for example, 194470 + ... + 194582.

It is an arithmetic number, because the mean of its divisors is an integer number (1020357).

Almost surely, 2^21981438 is an apocalyptic number.

21981438 is an abundant number, since it is smaller than the sum of its proper divisors (26995698).

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

21981438 is a wasteful number, since it uses less digits than its factorization.

21981438 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 329 (or 326 counting only the distinct ones).

The product of its digits is 13824, while the sum is 36.

The square root of 21981438 is about 4688.4366264246. The cubic root of 21981438 is about 280.1251056584.

The spelling of 21981438 in words is "twenty-one million, nine hundred eighty-one thousand, four hundred thirty-eight".