19978643 has 2 divisors, whose sum is σ = 19978644. Its totient is φ = 19978642.

The previous prime is 19978627. The next prime is 19978649. The reversal of 19978643 is 34687991.

It is a strong prime.

It is a cyclic number.

It is not a de Polignac number, because 19978643 - 2⁴ = 19978627 is a prime.

It is a super-2 number, since 2×19978643² = 798292352242898, which contains 22 as substring.

It is a Sophie Germain prime.

It is a Chen prime.

It is not a weakly prime, because it can be changed into another prime (19978649) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 9989321 + 9989322.

It is an arithmetic number, because the mean of its divisors is an integer number (9989322).

Almost surely, 2^19978643 is an apocalyptic number.

19978643 is a deficient number, since it is larger than the sum of its proper divisors (1).

19978643 is an equidigital number, since it uses as much as digits as its factorization.

19978643 is an evil number, because the sum of its binary digits is even.

The product of its digits is 326592, while the sum is 47.

The square root of 19978643 is about 4469.7475320201. The cubic root of 19978643 is about 271.3451075522.

The spelling of 19978643 in words is "nineteen million, nine hundred seventy-eight thousand, six hundred forty-three".