66400805 has 4 divisors (see below), whose sum is σ = 79680972. Its totient is φ = 53120640.

The previous prime is 66400787. The next prime is 66400813. The reversal of 66400805 is 50800466.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 50800466 = 2 ⋅25400233.

It can be written as a sum of positive squares in 2 ways, for example, as 41977441 + 24423364 = 6479^2 + 4942^2 .

It is not a de Polignac number, because 66400805 - 2¹⁴ = 66384421 is a prime.

It is a Duffinian number.

It is a congruent number.

It is an unprimeable number.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 6640076 + ... + 6640085.

It is an arithmetic number, because the mean of its divisors is an integer number (19920243).

Almost surely, 2^66400805 is an apocalyptic number.

It is an amenable number.

66400805 is a deficient number, since it is larger than the sum of its proper divisors (13280167).

66400805 is a wasteful number, since it uses less digits than its factorization.

66400805 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 13280166.

The product of its (nonzero) digits is 5760, while the sum is 29.

The square root of 66400805 is about 8148.6689097054. The cubic root of 66400805 is about 404.9404068187.

The spelling of 66400805 in words is "sixty-six million, four hundred thousand, eight hundred five".