66278561 has 2 divisors, whose sum is σ = 66278562. Its totient is φ = 66278560.

The previous prime is 66278557. The next prime is 66278573. The reversal of 66278561 is 16587266.

It is a weak prime.

It can be written as a sum of positive squares in only one way, i.e., 56550400 + 9728161 = 7520^2 + 3119^2 .

It is a cyclic number.

It is not a de Polignac number, because 66278561 - 2² = 66278557 is a prime.

It is not a weakly prime, because it can be changed into another prime (66278161) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 33139280 + 33139281.

It is an arithmetic number, because the mean of its divisors is an integer number (33139281).

Almost surely, 2^66278561 is an apocalyptic number.

It is an amenable number.

66278561 is a deficient number, since it is larger than the sum of its proper divisors (1).

66278561 is an equidigital number, since it uses as much as digits as its factorization.

66278561 is an evil number, because the sum of its binary digits is even.

The product of its digits is 120960, while the sum is 41.

The square root of 66278561 is about 8141.1645972797. The cubic root of 66278561 is about 404.6917554976.

The spelling of 66278561 in words is "sixty-six million, two hundred seventy-eight thousand, five hundred sixty-one".