66681340021 has 2 divisors, whose sum is σ = 66681340022. Its totient is φ = 66681340020.

The previous prime is 66681339961. The next prime is 66681340079. The reversal of 66681340021 is 12004318666.

It is a happy number.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 65441314225 + 1240025796 = 255815^2 + 35214^2 .

It is a cyclic number.

It is not a de Polignac number, because 66681340021 - 2⁹ = 66681339509 is a prime.

It is a super-2 number, since 2×66681340021² (a number of 22 digits) contains 22 as substring.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66481340021) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33340670010 + 33340670011.

It is an arithmetic number, because the mean of its divisors is an integer number (33340670011).

Almost surely, 2^66681340021 is an apocalyptic number.

It is an amenable number.

66681340021 is a deficient number, since it is larger than the sum of its proper divisors (1).

66681340021 is an equidigital number, since it uses as much as digits as its factorization.

66681340021 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 41472, while the sum is 37.

Adding to 66681340021 its reverse (12004318666), we get a palindrome (78685658687).

The spelling of 66681340021 in words is "sixty-six billion, six hundred eighty-one million, three hundred forty thousand, twenty-one".