66398813 has 4 divisors (see below), whose sum is σ = 71506428. Its totient is φ = 61291200.

The previous prime is 66398747. The next prime is 66398819. The reversal of 66398813 is 31889366.

It is a semiprime because it is the product of two primes.

It can be written as a sum of positive squares in 2 ways, for example, as 45941284 + 20457529 = 6778^2 + 4523^2 .

It is a cyclic number.

It is not a de Polignac number, because 66398813 - 2¹⁴ = 66382429 is a prime.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66398819) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 2553788 + ... + 2553813.

It is an arithmetic number, because the mean of its divisors is an integer number (17876607).

Almost surely, 2^66398813 is an apocalyptic number.

It is an amenable number.

66398813 is a deficient number, since it is larger than the sum of its proper divisors (5107615).

66398813 is a wasteful number, since it uses less digits than its factorization.

66398813 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5107614.

The product of its digits is 186624, while the sum is 44.

The square root of 66398813 is about 8148.5466802369. The cubic root of 66398813 is about 404.9363574233.

It can be divided in two parts, 663988 and 13, that multiplied together give a square (8631844 = 2938²).

The spelling of 66398813 in words is "sixty-six million, three hundred ninety-eight thousand, eight hundred thirteen".