665729921 has 2 divisors, whose sum is σ = 665729922. Its totient is φ = 665729920.

The previous prime is 665729861. The next prime is 665729951. The reversal of 665729921 is 129927566.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 386672896 + 279057025 = 19664^2 + 16705^2 .

It is a cyclic number.

It is not a de Polignac number, because 665729921 - 2²⁶ = 598621057 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (665729951) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 332864960 + 332864961.

It is an arithmetic number, because the mean of its divisors is an integer number (332864961).

Almost surely, 2^665729921 is an apocalyptic number.

It is an amenable number.

665729921 is a deficient number, since it is larger than the sum of its proper divisors (1).

665729921 is an equidigital number, since it uses as much as digits as its factorization.

665729921 is an evil number, because the sum of its binary digits is even.

The product of its digits is 408240, while the sum is 47.

The square root of 665729921 is about 25801.7425961891. The cubic root of 665729921 is about 873.1711115891.

The spelling of 665729921 in words is "six hundred sixty-five million, seven hundred twenty-nine thousand, nine hundred twenty-one".