I tried to calculate the number $f_3(3)$ with PARI/GP. It seems the number is too large to be calculated exactly. I would like to analyze the full decimal expansion.
Is there any trick to get all the digits ?
The number $f_3(3)$ is equal to $2^{402653211}\cdot 3$ having $121210695$ digits. I neither could display this number nor could I create the vector of its digits via "digits(n)". What can I do ?
UPDATE : I managed to store two numbers that could , concatenated , give the desired number. Of course, I cannot submit those numbers, but I will give the last digits of the first number and the first digits of the second number. I verfiied the first digits of the first number and the last digits of the second number. Apaarently, they are correct.
The last digits of the first number are
$$67339748680554085197019302058095933154479550517126426860727584719$$
The first number should be the integer part of the desired number divided by $10^{65\ 000\ 000}$
The first digits of the second number are $$811321643909024984450993111987746601114078967737295129933845859521$$
The second number should be the rest of the decimal expansion of the desired number. Can anyone approve those digits ?
The question is not about PARI/GP directly. Any computational system with sufficient time and storage could do the job. Essentially, you need to compute $a^bc$ for some positive integers $a,b,c$ using squaring and multiplication. First you need to decide how many decimal digits you can store in RAM comfortably. Let us use a million digits for concreteness. You just store the intermediate and final numbers in a collection of disk files, each having at most a million digits. To multiply $A*B$ use the standand radix representation multiplication algorithm on numbers, but in this case our radix is $R:=10^{\textrm{million}},$ a million decimal digits. We read two of the files to get $A_i$ and $B_j$, multiply them together and split the product into $A_i*B_j=C*R+D$ and add this to the accumulating partial product. PARI/GP and other similar programs do all this internally. Finally, the complete product will be stored on disk as a collection of files ready for further processing.
However, having written a general plan, I confess that PARI/GP is quite capable of computing the number in a few seconds. I used the statement $\;\texttt{n=3*2^402653211;}$ The size in bytes given by $\texttt{sizebyte(n)}$ is $50331660$. Actually getting the digits is another matter. The last $50$ digits using $\texttt{n%10^50}$ is $57619658951446422310193135419323844928197722374144$ which agrees with
You would get better answers by asking on the pari-users mailing list.
Edit: Note that for intermediate writing/reading disk it is important to use binary formats to avoid tremendous slowdown in converting to/from decimal. In PARI/GP that means using $\texttt{writebin()}$ instead of $\texttt{write()}.$