664890581 has 4 divisors (see below), whose sum is σ = 664961772. Its totient is φ = 664819392.

The previous prime is 664890559. The next prime is 664890613. The reversal of 664890581 is 185098466.

It is a semiprime because it is the product of two primes, and also a brilliant number, because the two primes have the same length.

It can be written as a sum of positive squares in 2 ways, for example, as 199798225 + 465092356 = 14135^2 + 21566^2 .

It is a cyclic number.

It is not a de Polignac number, because 664890581 - 2²² = 660696277 is a prime.

It is a super-2 number, since 2×664890581² = 884158969405035122, which contains 22 as substring.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (664892581) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 19010 + ... + 41123.

It is an arithmetic number, because the mean of its divisors is an integer number (166240443).

Almost surely, 2^664890581 is an apocalyptic number.

It is an amenable number.

664890581 is a deficient number, since it is larger than the sum of its proper divisors (71191).

664890581 is a wasteful number, since it uses less digits than its factorization.

664890581 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 71190.

The product of its (nonzero) digits is 414720, while the sum is 47.

The square root of 664890581 is about 25785.4722857659. The cubic root of 664890581 is about 872.8039979207.

The spelling of 664890581 in words is "six hundred sixty-four million, eight hundred ninety thousand, five hundred eighty-one".