66011821 has 4 divisors (see below), whose sum is σ = 67094044. Its totient is φ = 64929600.

The previous prime is 66011797. The next prime is 66011887. The reversal of 66011821 is 12811066.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12811066 = 2 ⋅6405533.

It can be written as a sum of positive squares in 2 ways, for example, as 11088900 + 54922921 = 3330^2 + 7411^2 .

It is a cyclic number.

It is not a de Polignac number, because 66011821 - 2¹⁹ = 65487533 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 (66011021) 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, 541020 + ... + 541141.

It is an arithmetic number, because the mean of its divisors is an integer number (16773511).

Almost surely, 2^66011821 is an apocalyptic number.

66011821 is a gapful number since it is divisible by the number (61) formed by its first and last digit.

It is an amenable number.

66011821 is a deficient number, since it is larger than the sum of its proper divisors (1082223).

66011821 is a wasteful number, since it uses less digits than its factorization.

66011821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 1082222.

The product of its (nonzero) digits is 576, while the sum is 25.

The square root of 66011821 is about 8124.7659043200. The cubic root of 66011821 is about 404.1481276413.

Adding to 66011821 its reverse (12811066), we get a palindrome (78822887).

The spelling of 66011821 in words is "sixty-six million, eleven thousand, eight hundred twenty-one".