66991601 has 2 divisors, whose sum is σ = 66991602. Its totient is φ = 66991600.

The previous prime is 66991567. The next prime is 66991607. The reversal of 66991601 is 10619966.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 49014001 + 17977600 = 7001^2 + 4240^2 .

It is a cyclic number.

It is not a de Polignac number, because 66991601 - 2¹⁰ = 66990577 is a prime.

It is not a weakly prime, because it can be changed into another prime (66991607) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33495800 + 33495801.

It is an arithmetic number, because the mean of its divisors is an integer number (33495801).

Almost surely, 2^66991601 is an apocalyptic number.

It is an amenable number.

66991601 is a deficient number, since it is larger than the sum of its proper divisors (1).

66991601 is an equidigital number, since it uses as much as digits as its factorization.

66991601 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 17496, while the sum is 38.

The square root of 66991601 is about 8184.8397052111. The cubic root of 66991601 is about 406.1378377222.

The spelling of 66991601 in words is "sixty-six million, nine hundred ninety-one thousand, six hundred one".