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A073755
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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(sqrt(n)) + 1, otherwise 2n - int(sqrt(n)) - 1; or -1 if no prime is ever reached.
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5
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10, 2, 1, 1, 9, 1, 1, 4, 2, 2, 5, 28, 3, 8, 1, 1, 1, 17, 2, 1, 27, 1, 1, 34, 7, 2, 4, 12, 4, 3, 2, 16, 2, 2, 1, 1, 1, 1, 12, 4, 9, 1, 33, 1, 6, 12, 1, 26, 2, 16, 11, 5, 21, 4, 2, 2, 6, 8, 15, 2, 3, 6, 1, 11, 3, 27, 2, 4, 1, 15, 2, 1, 1, 3, 12, 2, 2, 1, 8, 2, 7, 3, 6, 3, 16, 11, 4, 2, 25, 8, 4, 10
(list; graph; refs; listen; history; internal format)
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OFFSET
| 2,1
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EXAMPLE
| For n=3, a(3)=2 because 3 -> 4 -> 11
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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(sqrt(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(sqrt(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: A057603 A040097 A010174 * A010173 A136712 A138999
Adjacent sequences: A073752 A073753 A073754 * A073756 A073757 A073758
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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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