9978401666 has 4 divisors (see below), whose sum is σ = 14967602502. Its totient is φ = 4989200832.

The previous prime is 9978401663. The next prime is 9978401701. The reversal of 9978401666 is 6661048799.

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

It can be written as a sum of positive squares in only one way, i.e., 9215040025 + 763361641 = 95995^2 + 27629^2 .

It is not an unprimeable number, because it can be changed into a prime (9978401663) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (13) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 2494600415 + ... + 2494600418.

Almost surely, 2^9978401666 is an apocalyptic number.

9978401666 is a deficient number, since it is larger than the sum of its proper divisors (4989200836).

9978401666 is a wasteful number, since it uses less digits than its factorization.

9978401666 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 4989200835.

The product of its (nonzero) digits is 3919104, while the sum is 56.

The square root of 9978401666 is about 99891.9499559399. The cubic root of 9978401666 is about 2152.8824986695.

The spelling of 9978401666 in words is "nine billion, nine hundred seventy-eight million, four hundred one thousand, six hundred sixty-six".