6403981 has 2 divisors, whose sum is σ = 6403982. Its totient is φ = 6403980.

The previous prime is 6403979. The next prime is 6403993. The reversal of 6403981 is 1893046.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 6295081 + 108900 = 2509^2 + 330^2 .

It is a cyclic number.

It is not a de Polignac number, because 6403981 - 2¹ = 6403979 is a prime.

It is a super-2 number, since 2×6403981² = 82021945296722, which contains 22 as substring.

Together with 6403979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6403921) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 3201990 + 3201991.

It is an arithmetic number, because the mean of its divisors is an integer number (3201991).

Almost surely, 2^6403981 is an apocalyptic number.

It is an amenable number.

6403981 is a deficient number, since it is larger than the sum of its proper divisors (1).

6403981 is an equidigital number, since it uses as much as digits as its factorization.

6403981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 5184, while the sum is 31.

The square root of 6403981 is about 2530.6088200273. The cubic root of 6403981 is about 185.7020415427.

The spelling of 6403981 in words is "six million, four hundred three thousand, nine hundred eighty-one".