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Search: id:A093680
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| A093680 |
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Sequence contains no 3-term arithmetic progression, starting with 1,19. |
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+0
2
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| 1, 19, 20, 22, 23, 28, 29, 31, 32, 46, 47, 49, 50, 56, 58, 59, 82, 100, 101, 103, 104, 109, 110, 112, 113, 127, 128, 130, 131, 137, 139, 140, 244, 262, 263, 265, 266, 271, 272, 274, 275, 289, 290, 292, 293, 299, 301, 302, 325, 343, 344, 346, 347, 352, 353
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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a(1)=1, a(2)=19; a(n) is least k such that no three terms of a(1),a(2),...,a(n-1),k form an arithmetic progression.
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FORMULA
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a(n) = sum[k=1, n-1, (3^A007814(k)+1)/2] + f(n), with f(n) a 16-periodic function with values {1, 18, 17, 18, 14, 18, 17, 19, 5, 18, 17, 18, 14, 19, 19, 19, ...}, as proved by Lawrence Sze.
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CROSSREFS
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Cf. A004793, A033157, A093678-A093681, A092482.
Row 5 of array in A093682.
Sequence in context: A103418 A004508 A018824 this_sequence A007640 A054304 A022109
Adjacent sequences: A093677 A093678 A093679 this_sequence A093681 A093682 A093683
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KEYWORD
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nonn
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AUTHOR
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Ralf Stephan (ralf(AT)ark.in-berlin.de), Apr 09 2004
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