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%I #10 Sep 02 2013 03:48:20
%S 1,3,2,2,2,19,1,19,1,1,18,1,1,18,3,1,12,3,1,9,15,3,8,3,3,17,77,3,5,6,
%T 3,9,2,2,2,31,8,11,2,5,2,11,69,34,2,17,14,2,16,33,7,8,2,14,2,1,5,1,76,
%U 2,8,5,4,76,1,8,2,4,30,1,1,2,10,30,1,1,4,10,7,1,10,4,1,7,33,10,1,1,16,33
%N Number of steps needed to reach a prime when the following map is repeatedly applied to n: if n is even then 2n + int(log(n)) + 1, otherwise 2n - int(log(n)) - 1; or -1 if no prime is ever reached.
%o (UBASIC)
%o 10 cls
%o 30 for I=2 to 100
%o 32 H=I
%o 40 if odd(H)=1 then goto 90 else goto 50
%o 50 A=2*H+int(log(H))+1:K=K+1
%o 60 if prmdiv(A)=A then print I,K:goto 120
%o 65 if K>1000 then print I,0:goto 120
%o 70 H=A:goto 40
%o 90 A=2*H-int(log(H))-1:K=K+1
%o 100 if prmdiv(A)=A then print I,K:goto 120
%o 105 if K>1000 then print I,0:goto 120
%o 110 H=A:goto 40
%o 120 K=0
%o 130 next
%K easy,nonn
%O 2,2
%A _Felice Russo_, Sep 02 2002
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