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Search: id:A022266
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| 0, 4, 17, 39, 70, 110, 159, 217, 284, 360, 445, 539, 642, 754, 875, 1005, 1144, 1292, 1449, 1615, 1790, 1974, 2167, 2369, 2580, 2800, 3029, 3267, 3514, 3770, 4035, 4309, 4592, 4884, 5185, 5495, 5814, 6142
(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 0,4,... - 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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FORMULA
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a(n)=C(9*n,2)/9,n>=0 - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 02 2007
a(n)=A049452(n)-A000326(n). - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 12 2007
a(n)=9*n+a(n-1)-14 (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+0-14=4; n=3, a(3)=9*3+4-14=17; n=4, a(4)=9*4+17-14=39 [From Vincenzo Librandi (vincenzo.librandi(AT)tin.it), Nov 12 2009]
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MAPLE
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[seq(binomial(9*n, 2)/9, n=0..37)]; - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jan 02 2007
seq(n*(6*n-1)-n*(3*n-1)/2, n=0..37); - Zerinvary Lajos (zerinvarylajos(AT)yahoo.com), Jun 12 2007
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MATHEMATICA
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s=0; lst={s}; Do[s+=n++ +4; AppendTo[lst, s], {n, 0, 7!, 9}]; lst [From Vladimir Orlovsky (4vladimir(AT)gmail.com), Nov 16 2008]
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CROSSREFS
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Cf. A051682.
Sequence in context: A031092 A120884 A041859 this_sequence A145995 A018973 A162148
Adjacent sequences: A022263 A022264 A022265 this_sequence A022267 A022268 A022269
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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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