66001681 has 2 divisors, whose sum is σ = 66001682. Its totient is φ = 66001680.

The previous prime is 66001669. The next prime is 66001699. The reversal of 66001681 is 18610066.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 33454656 + 32547025 = 5784^2 + 5705^2 .

It is a cyclic number.

It is not a de Polignac number, because 66001681 - 2¹³ = 65993489 is a prime.

It is a super-2 number, since 2×66001681² = 8712443789651522, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (66001631) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33000840 + 33000841.

It is an arithmetic number, because the mean of its divisors is an integer number (33000841).

Almost surely, 2^66001681 is an apocalyptic number.

It is an amenable number.

66001681 is a deficient number, since it is larger than the sum of its proper divisors (1).

66001681 is an equidigital number, since it uses as much as digits as its factorization.

66001681 is an odious number, because the sum of its binary digits is odd.

The product of its (nonzero) digits is 1728, while the sum is 28.

The square root of 66001681 is about 8124.1418623754. The cubic root of 66001681 is about 404.1274330050.

It can be divided in two parts, 6600 and 1681, that added together give a square (8281 = 91²).

The spelling of 66001681 in words is "sixty-six million, one thousand, six hundred eighty-one".