66400081 has 6 divisors (see below), whose sum is σ = 72985346. Its totient is φ = 60363600.

The previous prime is 66400073. The next prime is 66400091. The reversal of 66400081 is 18000466.

It can be written as a sum of positive squares in only one way, i.e., 64657681 + 1742400 = 8041^2 + 1320^2 .

It is not a de Polignac number, because 66400081 - 2³ = 66400073 is a prime.

It is a super-2 number, since 2×66400081² = 8817941513613122, which contains 22 as substring.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66400021) by changing a digit.

It is a polite number, since it can be written in 5 ways as a sum of consecutive naturals, for example, 274260 + ... + 274501.

Almost surely, 2^66400081 is an apocalyptic number.

It is an amenable number.

66400081 is a deficient number, since it is larger than the sum of its proper divisors (6585265).

66400081 is a wasteful number, since it uses less digits than its factorization.

66400081 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 548783 (or 548772 counting only the distinct ones).

The product of its (nonzero) digits is 1152, while the sum is 25.

The square root of 66400081 is about 8148.6244851509. The cubic root of 66400081 is about 404.9389350599.

The spelling of 66400081 in words is "sixty-six million, four hundred thousand, eighty-one".