66671821 has 4 divisors (see below), whose sum is σ = 66826944. Its totient is φ = 66516700.

The previous prime is 66671809. The next prime is 66671831. The reversal of 66671821 is 12817666.

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 66671821 - 2¹¹ = 66669773 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 (66671831) 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, 76915 + ... + 77776.

It is an arithmetic number, because the mean of its divisors is an integer number (16706736).

Almost surely, 2^66671821 is an apocalyptic number.

It is an amenable number.

66671821 is a deficient number, since it is larger than the sum of its proper divisors (155123).

66671821 is a wasteful number, since it uses less digits than its factorization.

66671821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 155122.

The product of its digits is 24192, while the sum is 37.

The square root of 66671821 is about 8165.2814403424. The cubic root of 66671821 is about 405.4905826678.

The spelling of 66671821 in words is "sixty-six million, six hundred seventy-one thousand, eight hundred twenty-one".