16661172206391 has 4 divisors (see below), whose sum is σ = 22214896275192. Its totient is φ = 11107448137592.

The previous prime is 16661172206347. The next prime is 16661172206407. The reversal of 16661172206391 is 19360227116661.

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 16661172206391 - 2²¹ = 16661170109239 is a prime.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (16661172246391) 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, 2776862034396 + ... + 2776862034401.

It is an arithmetic number, because the mean of its divisors is an integer number (5553724068798).

Almost surely, 2^{16661172206391} is an apocalyptic number.

16661172206391 is a deficient number, since it is larger than the sum of its proper divisors (5553724068801).

16661172206391 is an equidigital number, since it uses as much as digits as its factorization.

16661172206391 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 5553724068800.

The product of its (nonzero) digits is 979776, while the sum is 51.

The spelling of 16661172206391 in words is "sixteen trillion, six hundred sixty-one billion, one hundred seventy-two million, two hundred six thousand, three hundred ninety-one".