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Jeopardy style (Posted on 2018-09-23) Difficulty: 3 of 5
Answer: To get the largest N-digit prime one only needs to subtract N from 10^N.

Jeopardy style question: What is N?

Your task : evaluate N.

See The Solution Submitted by Ady TZIDON    
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Some Thoughts another correct response Comment 2 of 2 |
n = 3 or n = 23

997 is the last prime before 1000

99999999999999999999977 is the last prime before 100000000000000000000000

   10   point 80
   20   for M=1 to 200 step 2
   30    if fnPrime(10^M-M) then
   40      :if fnNxPrime(10^M-M+1)>10^M then print M
   50   next
   80   end
   90   '
10000   fnOddfact(N)
10010   local K=0,P
10030   while N@2=0
10040     N=N\2
10050     K=K+1
10060   wend
10070   P=pack(N,K)
10080   return(P)
10090   '
10100   fnPrime(N)
10110   local I,X,J,Y,Q,K,T,Ans
10120   if N@2=0 then Ans=0:goto *EndPrime
10125   O=fnOddfact(N-1)
10130   Q=member(O,1)
10140   K=member(O,2)
10150   I=0
10160   repeat
10170     repeat
10180       X=fnLrand(N)
10190     until X>1
10200     J=0
10210     Y=modpow(X,Q,N)
10220     loop
10230       if or{and{J=0,Y=1},Y=N-1} then goto *ProbPrime
10240       if and{J>0,Y=1} then goto *NotPrime
10250       J=J+1
10260       if J=K then goto *NotPrime
10270       Y=(Y*Y)@N
10280     endloop
10290    *ProbPrime
10300     I=I+1
10310   until I>50
10320   Ans=1
10330   goto *EndPrime
10340   *NotPrime
10350   Ans=0
10360   *EndPrime
10370   return(Ans)
10380   '
10400   fnLrand(N)
10410   local R
10415   N=int(N)
10420   R=(int(rnd*10^(alen(N)+2)))@N
10430   return(R)
10440   '
10500   fnNxprime(X)
10510   if X@2=0 then X=X+1
10520   while fnPrime(X)=0
10530     X=X+2
10540   wend
10550   return(X)
10560   '


  Posted by Charlie on 2018-09-23 14:35:46
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