640981949 has 2 divisors, whose sum is σ = 640981950. Its totient is φ = 640981948.

The previous prime is 640981927. The next prime is 640981981. The reversal of 640981949 is 949189046.

It is a happy number.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 502566724 + 138415225 = 22418^2 + 11765^2 .

It is a cyclic number.

It is not a de Polignac number, because 640981949 - 2¹² = 640977853 is a prime.

It is a Sophie Germain prime.

It is a Curzon number.

It is a junction number, because it is equal to n+sod(n) for n = 640981897 and 640981906.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640981909) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320490974 + 320490975.

It is an arithmetic number, because the mean of its divisors is an integer number (320490975).

Almost surely, 2^640981949 is an apocalyptic number.

It is an amenable number.

640981949 is a deficient number, since it is larger than the sum of its proper divisors (1).

640981949 is an equidigital number, since it uses as much as digits as its factorization.

640981949 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 559872, while the sum is 50.

The square root of 640981949 is about 25317.6213140176. The cubic root of 640981949 is about 862.2143893365.

The spelling of 640981949 in words is "six hundred forty million, nine hundred eighty-one thousand, nine hundred forty-nine".