100643981 has 2 divisors, whose sum is σ = 100643982. Its totient is φ = 100643980.

The previous prime is 100643957. The next prime is 100643989. The reversal of 100643981 is 189346001.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 79941481 + 20702500 = 8941^2 + 4550^2 .

It is a cyclic number.

It is not a de Polignac number, because 100643981 - 2¹⁸ = 100381837 is a prime.

It is a super-2 number, since 2×100643981² = 20258421823056722, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Curzon number.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (100643989) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 50321990 + 50321991.

It is an arithmetic number, because the mean of its divisors is an integer number (50321991).

Almost surely, 2^100643981 is an apocalyptic number.

It is an amenable number.

100643981 is a deficient number, since it is larger than the sum of its proper divisors (1).

100643981 is an equidigital number, since it uses as much as digits as its factorization.

100643981 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 5184, while the sum is 32.

The square root of 100643981 is about 10032.1473773066. The cubic root of 100643981 is about 465.1531171863.

Adding to 100643981 its reverse (189346001), we get a palindrome (289989982).

The spelling of 100643981 in words is "one hundred million, six hundred forty-three thousand, nine hundred eighty-one".