66521907838 has 4 divisors (see below), whose sum is σ = 99782861760. Its totient is φ = 33260953918.

The previous prime is 66521907833. The next prime is 66521907853. The reversal of 66521907838 is 83870912566.

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

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (66521907833) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 16630476958 + ... + 16630476961.

It is an arithmetic number, because the mean of its divisors is an integer number (24945715440).

Almost surely, 2^66521907838 is an apocalyptic number.

66521907838 is a deficient number, since it is larger than the sum of its proper divisors (33260953922).

66521907838 is a wasteful number, since it uses less digits than its factorization.

66521907838 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 33260953921.

The product of its (nonzero) digits is 4354560, while the sum is 55.

The spelling of 66521907838 in words is "sixty-six billion, five hundred twenty-one million, nine hundred seven thousand, eight hundred thirty-eight".