66105821 has 4 divisors (see below), whose sum is σ = 66253500. Its totient is φ = 65958144.

The previous prime is 66105779. The next prime is 66105827. The reversal of 66105821 is 12850166.

It is a happy number.

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 46648900 + 19456921 = 6830^2 + 4411^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66105821 is a prime.

It is a Duffinian number.

It is a Curzon number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66105827) 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, 73166 + ... + 74063.

It is an arithmetic number, because the mean of its divisors is an integer number (16563375).

Almost surely, 2^66105821 is an apocalyptic number.

It is an amenable number.

66105821 is a deficient number, since it is larger than the sum of its proper divisors (147679).

66105821 is a wasteful number, since it uses less digits than its factorization.

66105821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 147678.

The product of its (nonzero) digits is 2880, while the sum is 29.

The square root of 66105821 is about 8130.5486284752. The cubic root of 66105821 is about 404.3398706013.

Adding to 66105821 its reverse (12850166), we get a palindrome (78955987).

The spelling of 66105821 in words is "sixty-six million, one hundred five thousand, eight hundred twenty-one".