636648781 has 2 divisors, whose sum is σ = 636648782. Its totient is φ = 636648780.

The previous prime is 636648743. The next prime is 636648833. The reversal of 636648781 is 187846636.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 431185225 + 205463556 = 20765^2 + 14334^2 .

It is a cyclic number.

It is not a de Polignac number, because 636648781 - 2⁹ = 636648269 is a prime.

It is a super-2 number, since 2×636648781² = 810643340697571922, which contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (636648731) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 318324390 + 318324391.

It is an arithmetic number, because the mean of its divisors is an integer number (318324391).

Almost surely, 2^636648781 is an apocalyptic number.

It is an amenable number.

636648781 is a deficient number, since it is larger than the sum of its proper divisors (1).

636648781 is an equidigital number, since it uses as much as digits as its factorization.

636648781 is an evil number, because the sum of its binary digits is even.

The product of its digits is 1161216, while the sum is 49.

The square root of 636648781 is about 25231.9000671769. The cubic root of 636648781 is about 860.2670799284.

The spelling of 636648781 in words is "six hundred thirty-six million, six hundred forty-eight thousand, seven hundred eighty-one".