66656021 has 4 divisors (see below), whose sum is σ = 66932844. Its totient is φ = 66379200.

The previous prime is 66655999. The next prime is 66656027. The reversal of 66656021 is 12065666.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 12065666 = 2 ⋅6032833.

It can be written as a sum of positive squares in 2 ways, for example, as 43375396 + 23280625 = 6586^2 + 4825^2 .

It is a cyclic number.

It is a de Polignac number, because none of the positive numbers 2^k-66656021 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 (66656027) 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, 138050 + ... + 138531.

It is an arithmetic number, because the mean of its divisors is an integer number (16733211).

Almost surely, 2^66656021 is an apocalyptic number.

It is an amenable number.

66656021 is a deficient number, since it is larger than the sum of its proper divisors (276823).

66656021 is a wasteful number, since it uses less digits than its factorization.

66656021 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 276822.

The product of its (nonzero) digits is 12960, while the sum is 32.

The square root of 66656021 is about 8164.3138719674. The cubic root of 66656021 is about 405.4585488576.

The spelling of 66656021 in words is "sixty-six million, six hundred fifty-six thousand, twenty-one".