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Search: id:A007742
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| 0, 5, 18, 39, 68, 105, 150, 203, 264, 333, 410, 495, 588, 689, 798, 915, 1040, 1173, 1314, 1463, 1620, 1785, 1958, 2139, 2328, 2525, 2730, 2943, 3164, 3393, 3630, 3875, 4128, 4389, 4658, 4935, 5220, 5513, 5814, 6123, 6440, 6765, 7098, 7439, 7788, 8145
(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,... in clockwise spiral; sequence gives numbers on positive y axis.
Central terms of the triangle in A126890. - Reinhard Zumkeller (reinhard.zumkeller(AT)gmail.com), Dec 30 2006
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REFERENCES
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S. M. Ellerstein, The square spiral, J. Recreational Mathematics 29 (#3, 1998) 188; 30 (#4, 1999-2000), 246-250.
R. L. Graham, D. E. Knuth and O. Patashnik, Concrete Mathematics. Addison-Wesley, Reading, MA, 2nd ed., 1994, p. 99.
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FORMULA
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G.f.: x(5+3x)/(1-x)^3. - Michael Somos, Mar 03 2003
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EXAMPLE
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Part of the spiral:
16 17 18 19 ...
15 4 5 6 ...
14 3 0 7 ...
13 2 1 8 ...
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PROGRAM
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(PARI) a(n)=4*n^2+n
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CROSSREFS
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a(n)=A033991(-n)=A074378(2n).
Sequences from spirals: A001107, A002939, A007742, A033951, A033952, A033953, A033954, A033989, A033990, A033991, A002943, A033996, A033988.
Adjacent sequences: A007739 A007740 A007741 this_sequence A007743 A007744 A007745
Sequence in context: A038346 A065007 A031428 this_sequence A000338 A056640 A101105
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KEYWORD
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nonn,easy,nice
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AUTHOR
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njas
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