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A123249
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a(1) = 1. For n >= 2, a(n) = n + (smallest integer which is >= n and is missing from among the earlier terms of the sequence).
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1
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1, 4, 6, 9, 10, 13, 14, 16, 20, 21, 22, 24, 28, 29, 30, 33, 34, 36, 38, 43, 44, 45, 46, 49, 50, 52, 54, 59, 60, 61, 62, 64, 68, 69, 70, 73, 74, 77, 78, 80, 82, 84, 90, 91, 92, 93, 94, 96, 100, 101, 102, 105, 106, 109, 110, 112, 114, 116, 122, 123, 124, 125, 126, 129, 130
(list; graph; refs; listen; history; internal format)
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OFFSET
| 1,2
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EXAMPLE
| 5 is the smallest integer which does not occur among the first 3 terms of the sequence and which is >= 4. So a(4) = 4 + 5 = 9.
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MATHEMATICA
| f[l_List] := Block[{n = Length[l] + 1, k = n}, While[MemberQ[l, k], k++ ]; Append[l, n + k]]; Nest[f, {1}, 70] (*Chandler*)
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PROG
| (PARI) {m=65; w=vector(3*m); print1(a=1, ", "); for(n=2, m, k=n; while(w[k], k++); print1(a=n+k, ", "); w[a]=1)} - (Klaus Brockhaus, Oct 09 2006)
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CROSSREFS
| Cf. A123088, A123721.
Sequence in context: A171401 A120329 A182800 * A171136 A189167 A010428
Adjacent sequences: A123246 A123247 A123248 * A123250 A123251 A123252
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KEYWORD
| easy,nonn
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AUTHOR
| Leroy Quet Oct 08 2006
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EXTENSIONS
| Corrected and extended by Klaus Brockhaus (klaus-brockhaus(AT)t-online.de) and Ray Chandler (rayjchandler(AT)sbcglobal.net), Oct 09 2006
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