66694781 has 2 divisors, whose sum is σ = 66694782. Its totient is φ = 66694780.

The previous prime is 66694753. The next prime is 66694799. The reversal of 66694781 is 18749666.

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., 66667225 + 27556 = 8165^2 + 166^2 .

It is a cyclic number.

It is not a de Polignac number, because 66694781 - 2¹⁸ = 66432637 is a prime.

It is a super-2 number, since 2×66694781² = 8896387625275922, which contains 22 as substring.

It is a Chen prime.

It is a congruent number.

It is not a weakly prime, because it can be changed into another prime (66690781) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (19) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33347390 + 33347391.

It is an arithmetic number, because the mean of its divisors is an integer number (33347391).

Almost surely, 2^66694781 is an apocalyptic number.

It is an amenable number.

66694781 is a deficient number, since it is larger than the sum of its proper divisors (1).

66694781 is an equidigital number, since it uses as much as digits as its factorization.

66694781 is an odious number, because the sum of its binary digits is odd.

The product of its digits is 435456, while the sum is 47.

The square root of 66694781 is about 8166.6872720828. The cubic root of 66694781 is about 405.5371240458.

The spelling of 66694781 in words is "sixty-six million, six hundred ninety-four thousand, seven hundred eighty-one".