661405609 has 2 divisors, whose sum is σ = 661405610. Its totient is φ = 661405608.

The previous prime is 661405583. The next prime is 661405631. The reversal of 661405609 is 906504166.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 635191209 + 26214400 = 25203^2 + 5120^2 .

It is a cyclic number.

It is not a de Polignac number, because 661405609 - 2⁹ = 661405097 is a prime.

It is equal to p_34355467 and since 661405609 and 34355467 have the same sum of digits, it is a Honaker prime.

It is not a weakly prime, because it can be changed into another prime (661405109) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 330702804 + 330702805.

It is an arithmetic number, because the mean of its divisors is an integer number (330702805).

Almost surely, 2^661405609 is an apocalyptic number.

It is an amenable number.

661405609 is a deficient number, since it is larger than the sum of its proper divisors (1).

661405609 is an equidigital number, since it uses as much as digits as its factorization.

661405609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 38880, while the sum is 37.

The square root of 661405609 is about 25717.8072354546. The cubic root of 661405609 is about 871.2764145942.

The spelling of 661405609 in words is "six hundred sixty-one million, four hundred five thousand, six hundred nine".