646201981 has 2 divisors, whose sum is σ = 646201982. Its totient is φ = 646201980.

The previous prime is 646201973. The next prime is 646201987. The reversal of 646201981 is 189102646.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 429111225 + 217090756 = 20715^2 + 14734^2 .

It is a cyclic number.

It is not a de Polignac number, because 646201981 - 2³ = 646201973 is a prime.

It is a super-2 number, since 2×646201981² = 835154000496648722, which contains 22 as substring.

It is a self number, because there is not a number n which added to its sum of digits gives 646201981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (646201987) 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, 323100990 + 323100991.

It is an arithmetic number, because the mean of its divisors is an integer number (323100991).

Almost surely, 2^646201981 is an apocalyptic number.

It is an amenable number.

646201981 is a deficient number, since it is larger than the sum of its proper divisors (1).

646201981 is an equidigital number, since it uses as much as digits as its factorization.

646201981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 20736, while the sum is 37.

The square root of 646201981 is about 25420.5031618180. The cubic root of 646201981 is about 864.5486328340.

The spelling of 646201981 in words is "six hundred forty-six million, two hundred one thousand, nine hundred eighty-one".