649691981 has 2 divisors, whose sum is σ = 649691982. Its totient is φ = 649691980.

The previous prime is 649691969. The next prime is 649691983. The reversal of 649691981 is 189196946.

It is a happy number.

649691981 is digitally balanced in base 2, because in such base it contains all the possibile digits an equal number of times.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 385336900 + 264355081 = 19630^2 + 16259^2 .

It is a cyclic number.

It is not a de Polignac number, because 649691981 - 2¹⁰ = 649690957 is a prime.

It is a super-2 number, since 2×649691981² = 844199340351408722, which contains 22 as substring.

Together with 649691983, it forms a pair of twin primes.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (649691983) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 324845990 + 324845991.

It is an arithmetic number, because the mean of its divisors is an integer number (324845991).

Almost surely, 2^649691981 is an apocalyptic number.

It is an amenable number.

649691981 is a deficient number, since it is larger than the sum of its proper divisors (1).

649691981 is an equidigital number, since it uses as much as digits as its factorization.

649691981 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 839808, while the sum is 53.

The square root of 649691981 is about 25489.0561025708. The cubic root of 649691981 is about 866.1022539254.

The spelling of 649691981 in words is "six hundred forty-nine million, six hundred ninety-one thousand, nine hundred eighty-one".