66691609 has 2 divisors, whose sum is σ = 66691610. Its totient is φ = 66691608.

The previous prime is 66691591. The next prime is 66691621. The reversal of 66691609 is 90619666.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 56957209 + 9734400 = 7547^2 + 3120^2 .

It is a cyclic number.

It is not a de Polignac number, because 66691609 - 2⁷ = 66691481 is a prime.

It is a super-2 number, since 2×66691609² = 8895541422017762, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (66691699) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33345804 + 33345805.

It is an arithmetic number, because the mean of its divisors is an integer number (33345805).

Almost surely, 2^66691609 is an apocalyptic number.

It is an amenable number.

66691609 is a deficient number, since it is larger than the sum of its proper divisors (1).

66691609 is an equidigital number, since it uses as much as digits as its factorization.

66691609 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 104976, while the sum is 43.

The square root of 66691609 is about 8166.4930661821. The cubic root of 66691609 is about 405.5306948363.

The spelling of 66691609 in words is "sixty-six million, six hundred ninety-one thousand, six hundred nine".