6643981 has 2 divisors, whose sum is σ = 6643982. Its totient is φ = 6643980.

The previous prime is 6643969. The next prime is 6643993. The reversal of 6643981 is 1893466.

It is a balanced prime because it is at equal distance from previous prime (6643969) and next prime (6643993).

It can be written as a sum of positive squares in only one way, i.e., 5522500 + 1121481 = 2350^2 + 1059^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6643981 is a prime.

It is a super-2 number, since 2×6643981² = 88284967056722, which contains 22 as substring.

It is a Chen prime.

It is a self number, because there is not a number n which added to its sum of digits gives 6643981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6643181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3321990 + 3321991.

It is an arithmetic number, because the mean of its divisors is an integer number (3321991).

Almost surely, 2^6643981 is an apocalyptic number.

It is an amenable number.

6643981 is a deficient number, since it is larger than the sum of its proper divisors (1).

6643981 is an equidigital number, since it uses as much as digits as its factorization.

6643981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 31104, while the sum is 37.

The square root of 6643981 is about 2577.5920934081. The cubic root of 6643981 is about 187.9934828735.

The spelling of 6643981 in words is "six million, six hundred forty-three thousand, nine hundred eighty-one".