661511509 has 2 divisors, whose sum is σ = 661511510. Its totient is φ = 661511508.

The previous prime is 661511503. The next prime is 661511551. The reversal of 661511509 is 905115166.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 333792900 + 327718609 = 18270^2 + 18103^2 .

It is a cyclic number.

It is not a de Polignac number, because 661511509 - 2¹¹ = 661509461 is a prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (661511503) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330755754 + 330755755.

It is an arithmetic number, because the mean of its divisors is an integer number (330755755).

Almost surely, 2^661511509 is an apocalyptic number.

It is an amenable number.

661511509 is a deficient number, since it is larger than the sum of its proper divisors (1).

661511509 is an equidigital number, since it uses as much as digits as its factorization.

661511509 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 8100, while the sum is 34.

The square root of 661511509 is about 25719.8660377538. The cubic root of 661511509 is about 871.3229131659.

The spelling of 661511509 in words is "six hundred sixty-one million, five hundred eleven thousand, five hundred nine".