66721821 has 16 divisors (see below), whose sum is σ = 94555584. Its totient is φ = 41704704.

The previous prime is 66721819. The next prime is 66721829. The reversal of 66721821 is 12812766.

It is not a de Polignac number, because 66721821 - 2¹ = 66721819 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66721829) by changing a digit.

It is a polite number, since it can be written in 15 ways as a sum of consecutive naturals, for example, 11766 + ... + 16488.

It is an arithmetic number, because the mean of its divisors is an integer number (5909724).

Almost surely, 2^66721821 is an apocalyptic number.

It is an amenable number.

66721821 is a deficient number, since it is larger than the sum of its proper divisors (27833763).

66721821 is a wasteful number, since it uses less digits than its factorization.

66721821 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5020.

The product of its digits is 8064, while the sum is 33.

The square root of 66721821 is about 8168.3426103464. The cubic root of 66721821 is about 405.5919221477.

The spelling of 66721821 in words is "sixty-six million, seven hundred twenty-one thousand, eight hundred twenty-one".