668899981 has 4 divisors (see below), whose sum is σ = 669088732. Its totient is φ = 668711232.

The previous prime is 668899967. The next prime is 668899991. The reversal of 668899981 is 189998866.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 114297481 + 554602500 = 10691^2 + 23550^2 .

It is a cyclic number.

It is not a de Polignac number, because 668899981 - 2¹⁷ = 668768909 is a prime.

It is a super-2 number, since 2×668899981² = 894854369163600722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (668899991) 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, 88956 + ... + 96181.

It is an arithmetic number, because the mean of its divisors is an integer number (167272183).

Almost surely, 2^668899981 is an apocalyptic number.

It is an amenable number.

668899981 is a deficient number, since it is larger than the sum of its proper divisors (188751).

668899981 is a wasteful number, since it uses less digits than its factorization.

668899981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 188750.

The product of its digits is 13436928, while the sum is 64.

The square root of 668899981 is about 25863.1007615096. The cubic root of 668899981 is about 874.5548673579.

The spelling of 668899981 in words is "six hundred sixty-eight million, eight hundred ninety-nine thousand, nine hundred eighty-one".