10 for X=1 to 999999
20 Y=2*X*(X+1)+1
30 if prmdiv(Y)=Y then
40 :if fnPalin(Y)=1 then print X,Y
45 if prmdiv(Y)=0 then print "x=";X;"y=";Y;" is too big":end
50 next
60 end
1000 fnPalin(N)
1010 T=1:S=cutspc(str(N))
1020 for I=1 to int(len(S)/2)
1030 if mid(S,I,1)<>mid(S,len(S)+1-I,1) then T=0
1040 next
1050 return(T)
finds
x expression
1 5
9 181
12 313
1262 3187813
x= 92682 y= 17180091613 is too big
The last line indicates that when x got to 92,682, the expression became 17,180,091,613, which is too large for the test of primality used in the program.
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Posted by Charlie
on 2013-12-30 17:45:16 |
computer solution