687631981 has 2 divisors, whose sum is σ = 687631982. Its totient is φ = 687631980.

The previous prime is 687631979. The next prime is 687631999. The reversal of 687631981 is 189136786.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 631516900 + 56115081 = 25130^2 + 7491^2 .

It is a cyclic number.

It is not a de Polignac number, because 687631981 - 2¹ = 687631979 is a prime.

It is a super-2 number, since 2×687631981² = 945675482587968722, which contains 22 as substring.

Together with 687631979, it forms a pair of twin primes.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (681631981) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 343815990 + 343815991.

It is an arithmetic number, because the mean of its divisors is an integer number (343815991).

Almost surely, 2^687631981 is an apocalyptic number.

It is an amenable number.

687631981 is a deficient number, since it is larger than the sum of its proper divisors (1).

687631981 is an equidigital number, since it uses as much as digits as its factorization.

687631981 is an evil number, because the sum of its binary digits is even.

The product of its digits is 435456, while the sum is 49.

The square root of 687631981 is about 26222.7378623972. The cubic root of 687631981 is about 882.6435576607.

The spelling of 687631981 in words is "six hundred eighty-seven million, six hundred thirty-one thousand, nine hundred eighty-one".