66643649 has 2 divisors, whose sum is σ = 66643650. Its totient is φ = 66643648.

The previous prime is 66643637. The next prime is 66643651. The reversal of 66643649 is 94634666.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 63888049 + 2755600 = 7993^2 + 1660^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66643649 is a prime.

Together with 66643651, it forms a pair of twin primes.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (66643609) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33321824 + 33321825.

It is an arithmetic number, because the mean of its divisors is an integer number (33321825).

Almost surely, 2^66643649 is an apocalyptic number.

It is an amenable number.

66643649 is a deficient number, since it is larger than the sum of its proper divisors (1).

66643649 is an equidigital number, since it uses as much as digits as its factorization.

66643649 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 559872, while the sum is 44.

The square root of 66643649 is about 8163.5561491301. The cubic root of 66643649 is about 405.4334616338.

The spelling of 66643649 in words is "sixty-six million, six hundred forty-three thousand, six hundred forty-nine".