636781 has 2 divisors, whose sum is σ = 636782. Its totient is φ = 636780.

The previous prime is 636773. The next prime is 636809. The reversal of 636781 is 187636.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 434281 + 202500 = 659^2 + 450^2 .

It is a cyclic number.

It is not a de Polignac number, because 636781 - 2³ = 636773 is a prime.

It is a super-2 number, since 2×636781² = 810980083922, which contains 22 as substring.

It is an alternating number because its digits alternate between even and odd.

It is a plaindrome in base 8.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (636721) 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, 318390 + 318391.

It is an arithmetic number, because the mean of its divisors is an integer number (318391).

2⁶³⁶⁷⁸¹ is an apocalyptic number.

It is an amenable number.

636781 is a deficient number, since it is larger than the sum of its proper divisors (1).

636781 is an equidigital number, since it uses as much as digits as its factorization.

636781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 6048, while the sum is 31.

The square root of 636781 is about 797.9855888423. The cubic root of 636781 is about 86.0326629130.

The spelling of 636781 in words is "six hundred thirty-six thousand, seven hundred eighty-one".