66745681 has 2 divisors, whose sum is σ = 66745682. Its totient is φ = 66745680.

The previous prime is 66745667. The next prime is 66745691. The reversal of 66745681 is 18654766.

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., 66569281 + 176400 = 8159^2 + 420^2 .

It is a cyclic number.

It is not a de Polignac number, because 66745681 - 2¹⁷ = 66614609 is a prime.

It is a super-2 number, since 2×66745681² = 8909971864307522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (66745631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33372840 + 33372841.

It is an arithmetic number, because the mean of its divisors is an integer number (33372841).

Almost surely, 2^66745681 is an apocalyptic number.

It is an amenable number.

66745681 is a deficient number, since it is larger than the sum of its proper divisors (1).

66745681 is an equidigital number, since it uses as much as digits as its factorization.

66745681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 241920, while the sum is 43.

The square root of 66745681 is about 8169.8029964008. The cubic root of 66745681 is about 405.6402635038.

It can be divided in two parts, 66745 and 681, that multiplied together give a triangular number (45453345 = T₉₅₃₄).

The spelling of 66745681 in words is "sixty-six million, seven hundred forty-five thousand, six hundred eighty-one".