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A073741
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Number of steps needed to reach a prime when the following map is repeatedly applied to n: if n is even then 2n+1, otherwise 2n-1; or -1 if no prime is ever reached.
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0
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1, 1, 2, 2, 1, 1, 1, 1, 2, 2, 3, 3, 1, 1, 4, 4, 1, 1, 1, 1, 2, 2, 2, 2, 1, 1, 2, 2, 1, 1, 3, 3, 2, 2, 1, 1, 5, 5, 4, 4, 3, 3, 1, 1, 8, 8, 1, 1, 1, 1, 6, 6, 1, 1, 1, 1, 2, 2, 2, 2, 7, 7, 2, 2, 5, 5, 1, 1, 2, 2, 3, 3, 1, 1, 4, 4, 1, 1, 3, 3, 10, 10, 2, 2, 1, 1, 2, 2, 1, 1, 7, 7, 582, 582, 1, 1, 1, 1, 2, 2, 2, 2
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,3
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EXAMPLE
| For n=4, a(4)=2 because 4 ->9 ->17
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PROG
| 10 cls 30 for I=2 to 100 32 H=I 40 if odd(H)=1 then goto 90 else goto 50 50 A=2*H+1:K=K+1 60 if prmdiv(A)=A then print I, K:goto 120 65 if K>10000 then print I, "no solution":goto 120 70 H=A:goto 40 90 A=2*H-1:K=K+1 100 if prmdiv(A)=A then print I, K:goto 120 105 if K>10000 then print I, "no solution":goto 120 110 H=A:goto 40 120 K=0 130 next
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CROSSREFS
| Sequence in context: A157129 A101615 A140193 * A071838 A157896 A156072
Adjacent sequences: A073738 A073739 A073740 * A073742 A073743 A073744
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KEYWORD
| easy,nonn
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AUTHOR
| Felice Russo (frusso(AT)micron.com), Sep 02 2002
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EXTENSIONS
| More terms from Jason Earls (zevi_35711(AT)yahoo.com), Sep 04 2002
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