66921623991 has 12 divisors (see below), whose sum is σ = 98912581768. Its totient is φ = 43576871184.

The previous prime is 66921623987. The next prime is 66921623999. The reversal of 66921623991 is 19932612966.

66921623991 is a `hidden beast` number, since 6 + 6 + 9 + 2 + 1 + 623 + 9 + 9 + 1 = 666.

It is not a de Polignac number, because 66921623991 - 2² = 66921623987 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 (66921623999) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (23) of ones.

It is a polite number, since it can be written in 11 ways as a sum of consecutive naturals, for example, 86461660 + ... + 86462433.

Almost surely, 2^66921623991 is an apocalyptic number.

66921623991 is a deficient number, since it is larger than the sum of its proper divisors (31990957777).

66921623991 is a wasteful number, since it uses less digits than its factorization.

66921623991 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 172924142 (or 172924139 counting only the distinct ones).

The product of its digits is 1889568, while the sum is 54.

The spelling of 66921623991 in words is "sixty-six billion, nine hundred twenty-one million, six hundred twenty-three thousand, nine hundred ninety-one".