66210721 has 4 divisors (see below), whose sum is σ = 69089472. Its totient is φ = 63331972.

The previous prime is 66210719. The next prime is 66210737. The reversal of 66210721 is 12701266.

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: 12701266 = 2 ⋅6350633.

It is not a de Polignac number, because 66210721 - 2¹ = 66210719 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66210701) 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, 1439341 + ... + 1439386.

It is an arithmetic number, because the mean of its divisors is an integer number (17272368).

Almost surely, 2^66210721 is an apocalyptic number.

It is an amenable number.

66210721 is a deficient number, since it is larger than the sum of its proper divisors (2878751).

66210721 is a wasteful number, since it uses less digits than its factorization.

66210721 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 2878750.

The product of its (nonzero) digits is 1008, while the sum is 25.

The square root of 66210721 is about 8136.9970505095. The cubic root of 66210721 is about 404.5536331010.

Adding to 66210721 its reverse (12701266), we get a palindrome (78911987).

The spelling of 66210721 in words is "sixty-six million, two hundred ten thousand, seven hundred twenty-one".