66669821 has 4 divisors (see below), whose sum is σ = 67149600. Its totient is φ = 66190044.

The previous prime is 66669791. The next prime is 66669839. The reversal of 66669821 is 12896666.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 12896666 = 2 ⋅6448333.

It is a cyclic number.

It is not a de Polignac number, because 66669821 - 2¹⁴ = 66653437 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 (66669851) 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, 239681 + ... + 239958.

It is an arithmetic number, because the mean of its divisors is an integer number (16787400).

Almost surely, 2^66669821 is an apocalyptic number.

It is an amenable number.

66669821 is a deficient number, since it is larger than the sum of its proper divisors (479779).

66669821 is a wasteful number, since it uses less digits than its factorization.

66669821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 479778.

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

The square root of 66669821 is about 8165.1589696711. The cubic root of 66669821 is about 405.4865280349.

The spelling of 66669821 in words is "sixty-six million, six hundred sixty-nine thousand, eight hundred twenty-one".