6642781 has 4 divisors (see below), whose sum is σ = 6733852. Its totient is φ = 6551712.

The previous prime is 6642763. The next prime is 6642793. The reversal of 6642781 is 1872466.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 1872466 = 2 ⋅936233.

It can be written as a sum of positive squares in 2 ways, for example, as 1602756 + 5040025 = 1266^2 + 2245^2 .

It is a cyclic number.

It is not a de Polignac number, because 6642781 - 2¹⁹ = 6118493 is a prime.

It is a super-2 number, since 2×6642781² = 88253078827922, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (6642281) 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 in 3 ways as a sum of consecutive naturals, for example, 45426 + ... + 45571.

It is an arithmetic number, because the mean of its divisors is an integer number (1683463).

Almost surely, 2^6642781 is an apocalyptic number.

It is an amenable number.

6642781 is a deficient number, since it is larger than the sum of its proper divisors (91071).

6642781 is an equidigital number, since it uses as much as digits as its factorization.

6642781 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 91070.

The product of its digits is 16128, while the sum is 34.

The square root of 6642781 is about 2577.3593075084. The cubic root of 6642781 is about 187.9821640692.

The spelling of 6642781 in words is "six million, six hundred forty-two thousand, seven hundred eighty-one".