66655681 has 2 divisors, whose sum is σ = 66655682. Its totient is φ = 66655680.

The previous prime is 66655669. The next prime is 66655703. The reversal of 66655681 is 18655666.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 39187600 + 27468081 = 6260^2 + 5241^2 .

It is a cyclic number.

It is not a de Polignac number, because 66655681 - 2¹¹ = 66653633 is a prime.

It is a super-2 number, since 2×66655681² = 8885959619147522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (66655661) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33327840 + 33327841.

It is an arithmetic number, because the mean of its divisors is an integer number (33327841).

Almost surely, 2^66655681 is an apocalyptic number.

It is an amenable number.

66655681 is a deficient number, since it is larger than the sum of its proper divisors (1).

66655681 is an equidigital number, since it uses as much as digits as its factorization.

66655681 is an evil number, because the sum of its binary digits is even.

The product of its digits is 259200, while the sum is 43.

The square root of 66655681 is about 8164.2930496155. The cubic root of 66655681 is about 405.4578594668.

The spelling of 66655681 in words is "sixty-six million, six hundred fifty-five thousand, six hundred eighty-one".