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A062725
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Write 0,1,2,3,4,... in a triangular spiral, then a(n) is the sequence found by reading the line from 0 in the direction 0,7,...
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3
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0, 7, 23, 48, 82, 125, 177, 238, 308, 387, 475, 572, 678, 793, 917, 1050, 1192, 1343, 1503, 1672, 1850, 2037, 2233, 2438, 2652, 2875, 3107, 3348, 3598, 3857, 4125, 4402, 4688, 4983, 5287, 5600, 5922, 6253, 6593, 6942, 7300, 7667, 8043, 8428, 8822, 9225
(list; graph; refs; listen; history; internal format)
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OFFSET
| 0,2
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FORMULA
| a(n) = n*(9n+5)/2
a(n)=9*n+a(n-1)-2 with a(0)=0 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Aug 07 2010]
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EXAMPLE
| The spiral begins:
..........15
........16..14
......17..3...13
....18..4...2...12
..19..5...0...1...11
20..6...7...8...9...10
a(1)=9*1+0-2=7; a(2)=9*2+7-2=23; a(3)=9*3+23-2=48 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Aug 07 2010]
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MATHEMATICA
| s=0; lst={s}; Do[s+=n++ +7; AppendTo[lst, s], {n, 0, 7!, 9}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Nov 16 2008]
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CROSSREFS
| Cf. A051682.
Sequence in context: A101789 A162290 A180044 * A147121 A098334 A038796
Adjacent sequences: A062722 A062723 A062724 * A062726 A062727 A062728
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KEYWORD
| nonn,easy
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AUTHOR
| Floor van Lamoen (fvlamoen(AT)hotmail.com), Jul 21 2001
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EXTENSIONS
| Formula that confused indices corrected by R. J. Mathar (mathar(AT)strw.leidenuniv.nl), Jun 04 2010
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