66637721 has 2 divisors, whose sum is σ = 66637722. Its totient is φ = 66637720.

The previous prime is 66637699. The next prime is 66637757. The reversal of 66637721 is 12773666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 63027721 + 3610000 = 7939^2 + 1900^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66637721 is a prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (66636721) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33318860 + 33318861.

It is an arithmetic number, because the mean of its divisors is an integer number (33318861).

Almost surely, 2^66637721 is an apocalyptic number.

It is an amenable number.

66637721 is a deficient number, since it is larger than the sum of its proper divisors (1).

66637721 is an equidigital number, since it uses as much as digits as its factorization.

66637721 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 63504, while the sum is 38.

The square root of 66637721 is about 8163.1930639916. The cubic root of 66637721 is about 405.4214400790.

The spelling of 66637721 in words is "sixty-six million, six hundred thirty-seven thousand, seven hundred twenty-one".