Hello, Malay!

The sum of is written and the sum of the digits of this number is written

and the process is repeated until a one-digit number is obtained.

What is this one-digit number?

The sum-of-digits means we are dealing with "digital roots"

. . . . . that the numbers are reduced modulo-9.

We can reduce the products as we work, rather than waiting until the final product.

Since

. . then:

Hence: .

Therefore: .

The one-digit number is

~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~

An alternate solution . . .

Consider the digit roots of consecutive powers of 2.

. . .

The digits roots have a six-digit cycle: 2-4-8-7-5-1.

Since

. . the digit root of is the fourth one: