66820821 has 4 divisors (see below), whose sum is σ = 89094432. Its totient is φ = 44547212.

The previous prime is 66820811. The next prime is 66820847. The reversal of 66820821 is 12802866.

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.

It is a cyclic number.

It is not a de Polignac number, because 66820821 - 2⁹ = 66820309 is a prime.

It is a super-2 number, since 2×66820821² = 8930044238228082, which contains 22 as substring.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66820811) 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, 11136801 + ... + 11136806.

It is an arithmetic number, because the mean of its divisors is an integer number (22273608).

Almost surely, 2^66820821 is an apocalyptic number.

It is an amenable number.

66820821 is a deficient number, since it is larger than the sum of its proper divisors (22273611).

66820821 is a wasteful number, since it uses less digits than its factorization.

66820821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 22273610.

The product of its (nonzero) digits is 9216, while the sum is 33.

The square root of 66820821 is about 8174.4003449794. The cubic root of 66820821 is about 405.7924250539.

The spelling of 66820821 in words is "sixty-six million, eight hundred twenty thousand, eight hundred twenty-one".