64999981 has 2 divisors, whose sum is σ = 64999982.
Its totient is φ = 64999980.
The previous prime is 64999943. The next prime is 65000011. The reversal of 64999981 is 18999946.
It is a strong prime.
It can be written as a sum of positive squares in only one way, i.e., 33246756 + 31753225 = 5766^2 + 5635^2
It is a cyclic number.
It is not a de Polignac number, because 64999981 - 27 = 64999853 is a prime.
It is a super-2 number, since 2×649999812 = 8449995060000722, which contains 22 as substring.
It is a congruent number.
It is not a weakly prime, because it can be changed into another prime (64999481) 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, 32499990 + 32499991.
It is an arithmetic number, because the mean of its divisors is an integer number (32499991).
Almost surely, 264999981 is an apocalyptic number.
It is an amenable number.
64999981 is a deficient number, since it is larger than the sum of its proper divisors (1).
64999981 is an equidigital number, since it uses as much as digits as its factorization.
64999981 is an odious number, because the sum of its binary digits is odd.
The product of its digits is 1259712, while the sum is 55.
The square root of 64999981 is about 8062.2565699685.
The cubic root of 64999981 is about 402.0725366826.
The spelling of 64999981 in words is "sixty-four million, nine hundred ninety-nine thousand, nine hundred eighty-one".