243639981 has 40 divisors (see below), whose sum is σ = 393611064. Its totient is φ = 149299200.

The previous prime is 243639967. The next prime is 243640013. The reversal of 243639981 is 189936342.

It is a happy number.

243639981 is a `hidden beast` number, since 2 + 4 + 3 + 639 + 9 + 8 + 1 = 666.

It can be written as a sum of positive squares in 4 ways, for example, as 147403881 + 96236100 = 12141^2 + 9810^2 .

It is not a de Polignac number, because 243639981 - 2⁷ = 243639853 is a prime.

It is a super-2 number, since 2×243639981² = 118720880683360722, which contains 22 as substring.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (243639181) by changing a digit.

It is a polite number, since it can be written in 39 ways as a sum of consecutive naturals, for example, 421965 + ... + 422541.

Almost surely, 2^243639981 is an apocalyptic number.

It is an amenable number.

243639981 is a deficient number, since it is larger than the sum of its proper divisors (149971083).

243639981 is a wasteful number, since it uses less digits than its factorization.

243639981 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 1003 (or 994 counting only the distinct ones).

The product of its digits is 279936, while the sum is 45.

The square root of 243639981 is about 15608.9711704519. The cubic root of 243639981 is about 624.5724914316.

The spelling of 243639981 in words is "two hundred forty-three million, six hundred thirty-nine thousand, nine hundred eighty-one".