19978642 has 4 divisors (see below), whose sum is σ = 29967966. Its totient is φ = 9989320.

The previous prime is 19978627. The next prime is 19978643. The reversal of 19978642 is 24687991.

It is a semiprime because it is the product of two primes, and also an emirpimes, since its reverse is a distinct semiprime: 24687991 = 37 ⋅667243.

It can be written as a sum of positive squares in only one way, i.e., 10374841 + 9603801 = 3221^2 + 3099^2 .

It is a super-2 number, since 2×19978642² = 798292272328328, which contains 22 as substring.

It is a junction number, because it is equal to n+sod(n) for n = 19978592 and 19978601.

It is not an unprimeable number, because it can be changed into a prime (19978643) by changing a digit.

It is a pernicious number, because its binary representation contains a prime number (11) of ones.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 4994659 + ... + 4994662.

Almost surely, 2^19978642 is an apocalyptic number.

19978642 is a deficient number, since it is larger than the sum of its proper divisors (9989324).

19978642 is an equidigital number, since it uses as much as digits as its factorization.

19978642 is an odious number, because the sum of its binary digits is odd.

The sum of its prime factors is 9989323.

The product of its digits is 217728, while the sum is 46.

The square root of 19978642 is about 4469.7474201570. The cubic root of 19978642 is about 271.3451030250.

The spelling of 19978642 in words is "nineteen million, nine hundred seventy-eight thousand, six hundred forty-two".