19918186978 has 4 divisors (see below), whose sum is σ = 29877280470. Its totient is φ = 9959093488.

The previous prime is 19918186931. The next prime is 19918186987. The reversal of 19918186978 is 87968181991.

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., 16446267049 + 3471919929 = 128243^2 + 58923^2 .

It is a Smith number, since the sum of its digits (67) coincides with the sum of the digits of its prime factors. Since it is squarefree, it is also a hoax number.

It is an unprimeable number.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4979546743 + ... + 4979546746.

Almost surely, 2^19918186978 is an apocalyptic number.

19918186978 is a deficient number, since it is larger than the sum of its proper divisors (9959093492).

19918186978 is an equidigital number, since it uses as much as digits as its factorization.

19918186978 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 9959093491.

The product of its digits is 15676416, while the sum is 67.

The spelling of 19918186978 in words is "nineteen billion, nine hundred eighteen million, one hundred eighty-six thousand, nine hundred seventy-eight".