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Search: id:A022267
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| 0, 5, 19, 42, 74, 115, 165, 224, 292, 369, 455, 550, 654, 767, 889, 1020, 1160, 1309, 1467, 1634, 1810, 1995, 2189, 2392, 2604, 2825, 3055, 3294, 3542, 3799, 4065, 4340, 4624, 4917, 5219, 5530, 5850, 6179
(list; graph; listen)
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OFFSET
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0,2
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COMMENT
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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 0,5,... - Floor van Lamoen (fvlamoen(AT)hotmail.com), Jul 21 2001. The spiral begins:
..........15
........16..14
......17..3...13
....18..4...2...12
..19..5...0...1...11
20..6...7...8...9...10
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LINKS
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Milan Janjic, Two Enumerative Functions
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FORMULA
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a(n)=9*n+a(n-1)-13 (with a(1)=0) [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
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EXAMPLE
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For n=2, a(2)=9*2+0-13=5; n=3, a(3)=9*3+5-13=19; n=4, a(4)=9*4+19-13=42 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
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MAPLE
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seq(binomial(9*n+1, 2)/9, n=0..37); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 21 2007
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MATHEMATICA
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s=0; lst={s}; Do[s+=n++ +5; AppendTo[lst, s], {n, 0, 5!, 9}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Nov 16 2008]
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CROSSREFS
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Cf. A051682.
a(n) = A110449(n, 4) for n>3.
Sequence in context: A147307 A089148 A098319 this_sequence A094465 A020580 A146616
Adjacent sequences: A022264 A022265 A022266 this_sequence A022268 A022269 A022270
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KEYWORD
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nonn,new
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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