66721651 has 4 divisors (see below), whose sum is σ = 70646472. Its totient is φ = 62796832.

The previous prime is 66721639. The next prime is 66721657. The reversal of 66721651 is 15612766.

It is a happy number.

It is a semiprime because it is the product of two primes.

It is a cyclic number.

It is not a de Polignac number, because 66721651 - 2⁹ = 66721139 is a prime.

It is a Duffinian number.

It is not an unprimeable number, because it can be changed into a prime (66721657) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (17) of ones.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 1962385 + ... + 1962418.

It is an arithmetic number, because the mean of its divisors is an integer number (17661618).

Almost surely, 2^66721651 is an apocalyptic number.

66721651 is a deficient number, since it is larger than the sum of its proper divisors (3924821).

66721651 is a wasteful number, since it uses less digits than its factorization.

66721651 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 3924820.

The product of its digits is 15120, while the sum is 34.

The square root of 66721651 is about 8168.3322043120. The cubic root of 66721651 is about 405.5915776793.

The spelling of 66721651 in words is "sixty-six million, seven hundred twenty-one thousand, six hundred fifty-one".