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%I #4 Oct 01 2013 17:57:36
%S 17,23,31,37,41,61,67,73,83,109,131,163,179,197,229,233,239,257,263,
%T 277,293,311,313,331,337,349,389,439,443,449,457,467,491,521,523,557,
%U 577,587,599,641,659,661,673,677,701,739,743,757,761,769,773,787,829,877
%N Primes that terminate at 68,34,17 in the 3x-1 problem: Repeat, if x is even divide by 2 else multiply by 3 and subtract 1, until 17 is reached.
%o (PARI) px3nm1(n,p) = { forprime(x=2,n, p1 = x; while(p1>1, if(p1%2==0,p1/=2,p1 = p1*p-1;); if(p1 == 5 || p1==17,break); ); if(p1 == 17,print1(x" ")) ) }
%K easy,nonn
%O 1,1
%A _Cino Hilliard_, Mar 27 2003