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A073756
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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 + int(ln(n)) + 1, otherwise 2n - int(ln(n)) - 1; or -1 if no prime is ever reached.
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5
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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, 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, 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
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,2
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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+int(log(H))+1:K=K+1 60 if prmdiv(A)=A then print I, K:goto 120 65 if K>1000 then print I, 0:goto 120 70 H=A:goto 40 90 A=2*H-int(log(H))-1:K=K+1 100 if prmdiv(A)=A then print I, K:goto 120 105 if K>1000 then print I, 0:goto 120 110 H=A:goto 40 120 K=0 130 next
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CROSSREFS
| Sequence in context: A202538 A065437 A097721 * A006379 A105198 A133882
Adjacent sequences: A073753 A073754 A073755 * A073757 A073758 A073759
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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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