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Search: id:A114801
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| A114801 |
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2-concatenation-free sequence starting (1,2). |
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+0
1
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| 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 20, 100, 121, 122, 123, 124, 125, 126, 127, 128, 129, 130, 131, 132, 133, 134, 135, 136, 137, 138, 139, 140, 141, 142, 143, 144, 145, 146, 147, 148, 149, 150, 151, 152, 153, 154, 155, 156, 157, 158, 159, 160, 161, 162, 163, 164
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Starting with the terms (1,2) this sequence consists of minimum increasing terms such that no term is the concatenation of any two previous terms. The next consecutive number skipped after 121 is 201 = Concatenate(20,1); the sequence then resumes with 212, and is consecutive until skipping 220 = Concatenate(2,20). This is the analogue of a 2-Stoehr sequence with concatenation (base 10) substituting for addition. A033627 "0-additive sequence: not the sum of any previous pair" is another name for the 2-Stoehr sequence. Stoehr is actually spelled St[o with umlaut]hr.
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LINKS
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Eric Weisstein's World of Mathematics, Stoehr Sequence.
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FORMULA
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a(0) = 1, a(1) = 2, for n>2: a(n) = least k > a(n-1) such that k is not an element of {Concatenate(a(i),a(j))} for any distinct a(i)<a(n-1) and a(j)<a(n-1).
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CROSSREFS
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Cf. A084383, A033627.
Sequence in context: A055933 A132578 A101318 this_sequence A114802 A130575 A068637
Adjacent sequences: A114798 A114799 A114800 this_sequence A114802 A114803 A114804
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KEYWORD
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base,easy,nonn
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AUTHOR
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Jonathan Vos Post (jvospost3(AT)gmail.com), Feb 18 2006
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