21843981 has 6 divisors (see below), whose sum is σ = 31552430. Its totient is φ = 14562648.

The previous prime is 21843979. The next prime is 21844001. The reversal of 21843981 is 18934812.

21843981 is a `hidden beast` number, since 218 + 439 + 8 + 1 = 666.

It can be written as a sum of positive squares in only one way, i.e., 20331081 + 1512900 = 4509^2 + 1230^2 .

It is not a de Polignac number, because 21843981 - 2¹ = 21843979 is a prime.

It is a super-2 number, since 2×21843981² = 954319011856722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (21843911) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 1213546 + ... + 1213563.

Almost surely, 2^21843981 is an apocalyptic number.

It is an amenable number.

21843981 is a deficient number, since it is larger than the sum of its proper divisors (9708449).

21843981 is a wasteful number, since it uses less digits than its factorization.

21843981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2427115 (or 2427112 counting only the distinct ones).

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

The square root of 21843981 is about 4673.7544864916. The cubic root of 21843981 is about 279.5399801787.

The spelling of 21843981 in words is "twenty-one million, eight hundred forty-three thousand, nine hundred eighty-one".