665521709 has 2 divisors, whose sum is σ = 665521710. Its totient is φ = 665521708.

The previous prime is 665521697. The next prime is 665521771. The reversal of 665521709 is 907125566.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 629257225 + 36264484 = 25085^2 + 6022^2 .

It is a cyclic number.

It is not a de Polignac number, because 665521709 - 2¹² = 665517613 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (665551709) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332760854 + 332760855.

It is an arithmetic number, because the mean of its divisors is an integer number (332760855).

Almost surely, 2^665521709 is an apocalyptic number.

It is an amenable number.

665521709 is a deficient number, since it is larger than the sum of its proper divisors (1).

665521709 is an equidigital number, since it uses as much as digits as its factorization.

665521709 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 113400, while the sum is 41.

The square root of 665521709 is about 25797.7074369022. The cubic root of 665521709 is about 873.0800718373.

The spelling of 665521709 in words is "six hundred sixty-five million, five hundred twenty-one thousand, seven hundred nine".