6421781 has 2 divisors, whose sum is σ = 6421782. Its totient is φ = 6421780.

The previous prime is 6421777. The next prime is 6421783. The reversal of 6421781 is 1871246.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 6421156 + 625 = 2534^2 + 25^2 .

It is a cyclic number.

It is not a de Polignac number, because 6421781 - 2² = 6421777 is a prime.

It is a super-2 number, since 2×6421781² = 82478542423922, which contains 22 as substring.

Together with 6421783, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (6421783) 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, 3210890 + 3210891.

It is an arithmetic number, because the mean of its divisors is an integer number (3210891).

Almost surely, 2^6421781 is an apocalyptic number.

It is an amenable number.

6421781 is a deficient number, since it is larger than the sum of its proper divisors (1).

6421781 is an equidigital number, since it uses as much as digits as its factorization.

6421781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 2688, while the sum is 29.

The square root of 6421781 is about 2534.1233198090. The cubic root of 6421781 is about 185.8739366235.

The spelling of 6421781 in words is "six million, four hundred twenty-one thousand, seven hundred eighty-one".