631681 has 2 divisors, whose sum is σ = 631682. Its totient is φ = 631680.

The previous prime is 631679. The next prime is 631711. The reversal of 631681 is 186136.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 512656 + 119025 = 716^2 + 345^2 .

It is a cyclic number.

It is not a de Polignac number, because 631681 - 2¹ = 631679 is a prime.

It is a super-2 number, since 2×631681² = 798041771522, which contains 22 as substring.

Together with 631679, it forms a pair of twin primes.

631681 is a lucky number.

It is not a weakly prime, because it can be changed into another prime (631181) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 315840 + 315841.

It is an arithmetic number, because the mean of its divisors is an integer number (315841).

2⁶³¹⁶⁸¹ is an apocalyptic number.

It is an amenable number.

631681 is a deficient number, since it is larger than the sum of its proper divisors (1).

631681 is an equidigital number, since it uses as much as digits as its factorization.

631681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 864, while the sum is 25.

The square root of 631681 is about 794.7836183516. The cubic root of 631681 is about 85.8023675231.

The spelling of 631681 in words is "six hundred thirty-one thousand, six hundred eighty-one".