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A139080
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a(1)=1. a(n) = the smallest positive integer not occurring earlier in the sequence such that floor(max(a(n),a(n-1))/min(a(n),a(n-1))) = 2.
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1
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1, 2, 4, 8, 3, 6, 12, 5, 10, 20, 7, 14, 28, 11, 22, 9, 18, 36, 13, 26, 52, 19, 38, 15, 30, 60, 21, 42, 16, 32, 64, 23, 46, 17, 34, 68, 24, 48, 96, 33, 66, 25, 50, 100, 35, 70, 27, 54, 108, 37, 74, 29, 58, 116, 39, 78, 31, 62, 124, 43, 86, 40, 80, 160, 55, 110, 41, 82, 164, 56
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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COMMENTS
| Is there always an unused positive integer, a(n), such that floor(max(a(n),a(n-1))/min(a(n),a(n-1))) = 2, or does the sequence terminate? If the sequence is infinite, is it a permutation of the positive integers?
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LINKS
| M. F. Hasler, Table of n, a(n) for n=1,...,10000.
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PROG
| (PARI) { t=0; last=1; for( n=1, 10000, write("b139080.txt", n, " ", last); t+=1<<last; for( i=last\3+1, last\2, bittest(t, i) & next; last=i; next(2)); for( i=last*2, last*3-1, bittest(t, i) & next; last=i; next(2)); error("THE END: n=", n)); print("Largest term used:"); log(t)\log(2)} - M. F. Hasler (www.univ-ag.fr/~mhasler), Apr 07 2008
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CROSSREFS
| Sequence in context: A167203 A086317 A110217 * A036118 A101942 A050170
Adjacent sequences: A139077 A139078 A139079 * A139081 A139082 A139083
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KEYWORD
| nonn
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AUTHOR
| Leroy Quet Apr 07 2008
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EXTENSIONS
| Additional terms calculated by Robert Israel and Maximilian Hasler, Apr 11 2008
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