Courtesy Fabrice Bellard, here is a compact computer program in C to print out the world's largest known prime.

int m=167772161,N=1,t[1<<25]={2},a,*p,i,e=34893349,s,c,U=1;g(d,h){for(i=s;i<1<<24;i*=2)d=d*1LL*d%m;for(p=t;p<t+N;p+=s)for(i=s,c=1;i;i--)a=p[s ]*(h?c:1LL)%m,p[s]=(m+*p-a)*(h?1LL:c)%m,a+=*p,*p++=a%m,c=c*1LL*d%m;}main(){while(e /=2){N*=2;U=U*1LL*(m+1)/2%m;for(s=N;s/=2;)g(17,0);for(p=t;p<t+N;p++)*p=*p*1LL**p%m*U%m;for(s=1;s<N;s*=2)g(29606852,1);for(a=0,p=t;p<t+N;)a+=*p<<(e&1),*p++=a%10,a/=10;}while(!*--p);for(t[0]--;p>=t;)putchar(48+*p--);}

The program is just 438 characters in length. It compiles quite quickly on the MacBook Pro and requires less than 5 minutes of running time.

This number, the largest known prime, belongs to a class of primes called Mersenne primes and has the value 2

^{43112609}-1. It has no less than 13 million digits. I ran the program earlier today, and have pasted the first ten lines or so of the output below. I have a little mnemonic scheme to remember long strings of numbers and so I created a mnemonic to remember the first ten digits of the number. And so if you ever wanted to commit to memory the digits of the world's largest prime, you can start right here :
3164702693302559231434537239493375160541061884752646441403041767328112474930693686920431851216118378567268165399854650973561234326451796738535905772381793579008764261039437823764945917429345884971175871469169729847611590608732509394620855757407545770986205580117795298840421982876433193304650644552349881421395657854474740235463537585373248018381203876008684165254007903812858882566870858554562315775279393059208117665853086701321291552218043815486257879430206945280159992217181915577617890385395223497468087974769076640506012484732068741331946635853349838057348036207057782709105617167676809548144153100345024404451613323636117493261633464445423329417241203651488922044206753025635343930446888594451731619345493103361168211788553755310414238217064307960122462880374834762183969829160738164510589918315126863274884595850432467781607888733436616846762580064365828402220637577850480773894049127470626486721860033497517827818791204700203888737795893495898771199542833432881998869365937322503203399986100723393812928335949193182946075856105924454460588729823350956671321271750144252181252144132310783719856...

And so that brings me to the puzzle for this month. What is the last digit of the above prime number? It is not a very difficult puzzle, but it might take some thinking.

And so, enjoy your day. And happy solving!