640072981 has 2 divisors, whose sum is σ = 640072982. Its totient is φ = 640072980.

The previous prime is 640072963. The next prime is 640072991. The reversal of 640072981 is 189270046.

640072981 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., 568822500 + 71250481 = 23850^2 + 8441^2 .

It is a cyclic number.

It is not a de Polignac number, because 640072981 - 2²¹ = 637975829 is a prime.

It is a super-2 number, since 2×640072981² = 819386842012452722, 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 640072981.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (640072991) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 320036490 + 320036491.

It is an arithmetic number, because the mean of its divisors is an integer number (320036491).

Almost surely, 2^640072981 is an apocalyptic number.

It is an amenable number.

640072981 is a deficient number, since it is larger than the sum of its proper divisors (1).

640072981 is an equidigital number, since it uses as much as digits as its factorization.

640072981 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 24192, while the sum is 37.

The square root of 640072981 is about 25299.6636538907. The cubic root of 640072981 is about 861.8066316007.

The spelling of 640072981 in words is "six hundred forty million, seventy-two thousand, nine hundred eighty-one".