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Search: id:A077220
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| A077220 |
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a(1)=1; a(n) is the least positive number d not yet in the sequence such that a(n-1)+d is a triangular number. |
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+0
2
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| 1, 2, 4, 6, 9, 12, 3, 7, 8, 13, 15, 21, 24, 31, 5, 10, 11, 17, 19, 26, 29, 16, 20, 25, 30, 36, 42, 49, 56, 22, 14, 41, 37, 18, 27, 28, 38, 40, 51, 54, 66, 39, 52, 53, 67, 69, 84, 87, 33, 45, 46, 32, 23, 43, 35, 70, 50, 55, 65, 71, 34, 44, 47, 58, 62, 74, 79, 57, 48, 72, 64, 89
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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A rearrangement of the natural numbers, with inverse permutation A099130. The first few fixed points are: 1, 2, 19, 92, 220, 467, 556, 616, 690, 842.
Integer permutation with inverse A099130. - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 28 2004
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LINKS
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Zak Seidov, Table of n, a(n) for n = 1..1000
Index entries for sequences that are permutations of the natural numbers
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EXAMPLE
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n=5: ss={1,2,4,6}; triangular numbers > 6 are 10,15,21; but 10-6=4 is in ss, hence a(5)=15-6=9;
n=6, ss={1,2,4,6,9}; triangular numbers > 9 are 10,15,21; but 10-9=4 and 15-9=6 are in ss, hence a(6)=21-9=12 etc.
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CROSSREFS
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Cf. A000217, A125595, A125630.
Adjacent sequences: A077217 A077218 A077219 this_sequence A077221 A077222 A077223
Sequence in context: A022760 A054519 A038107 this_sequence A128716 A025057 A030763
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KEYWORD
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nonn
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AUTHOR
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Amarnath Murthy (amarnath_murthy(AT)yahoo.com), Nov 03 2002
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EXTENSIONS
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More terms from Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Sep 28 2004
Edited by njas at the suggestion of Andrew Plewe, Jun 08 2007
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