6643781 has 2 divisors, whose sum is σ = 6643782. Its totient is φ = 6643780.

The previous prime is 6643739. The next prime is 6643789. The reversal of 6643781 is 1873466.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 4708900 + 1934881 = 2170^2 + 1391^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-6643781 is a prime.

It is a super-2 number, since 2×6643781² = 88279651951922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6643789) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3321890 + 3321891.

It is an arithmetic number, because the mean of its divisors is an integer number (3321891).

Almost surely, 2^6643781 is an apocalyptic number.

It is an amenable number.

6643781 is a deficient number, since it is larger than the sum of its proper divisors (1).

6643781 is an equidigital number, since it uses as much as digits as its factorization.

6643781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 24192, while the sum is 35.

The square root of 6643781 is about 2577.5532972181. The cubic root of 6643781 is about 187.9915965008.

The spelling of 6643781 in words is "six million, six hundred forty-three thousand, seven hundred eighty-one".