19978866 has 16 divisors (see below), whose sum is σ = 44397600. Its totient is φ = 6659604.

The previous prime is 19978843. The next prime is 19978867. The reversal of 19978866 is 66887991.

It is a Smith number, since the sum of its digits (54) coincides with the sum of the digits of its prime factors.

It is a Harshad number since it is a multiple of its sum of digits (54), and also a Moran number because the ratio is a prime number: 369979 = 19978866 / (1 + 9 + 9 + 7 + 8 + 8 + 6 + 6).

It is a Curzon number.

It is not an unprimeable number, because it can be changed into a prime (19978867) by changing a digit.

It is a polite number, since it can be written in 7 ways as a sum of consecutive naturals, for example, 184936 + ... + 185043.

It is an arithmetic number, because the mean of its divisors is an integer number (2774850).

Almost surely, 2^19978866 is an apocalyptic number.

19978866 is an abundant number, since it is smaller than the sum of its proper divisors (24418734).

It is a pseudoperfect number, because it is the sum of a subset of its proper divisors.

19978866 is a wasteful number, since it uses less digits than its factorization.

19978866 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 369990 (or 369984 counting only the distinct ones).

The product of its digits is 1306368, while the sum is 54.

The square root of 19978866 is about 4469.7724774310. The cubic root of 19978866 is about 271.3461171259.

The spelling of 19978866 in words is "nineteen million, nine hundred seventy-eight thousand, eight hundred sixty-six".