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Search: id:A131098
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| 1, 3, 7, 11, 15, 19, 23, 27, 31, 35, 39, 43, 47, 51, 55, 59, 63, 67, 71, 75, 79, 83, 87, 91, 95, 99, 103, 107, 111, 115, 119, 123, 127, 131, 135, 139, 143, 147, 151, 155, 159, 163, 167, 171, 175, 179, 183, 187, 191, 195, 199, 203, 207, 211, 215, 219, 223, 227, 231, 235, 239
(list; graph; listen)
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OFFSET
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1,2
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COMMENT
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Draw 1 circle: we see 1 region. Draw 2 identical circles, the second with center on the other, we see 3 regions. Draw 3 identical the third with centre on both the others, we see 7 regions, ...
a(1) = 1, a(n+1) = 4n - 1 = sum of n-th odd natural number and n-th even natural number = A005408(n-1) + A005843(n) for n >= 1. [From Jaroslav Krizek (jaroslav.krizek(AT)atlas.cz), Aug 15 2009]
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CROSSREFS
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Sequence in context: A059554 A103543 A004767 this_sequence A118894 A039957 A079422
Adjacent sequences: A131095 A131096 A131097 this_sequence A131099 A131100 A131101
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KEYWORD
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nonn
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AUTHOR
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Hans Isdahl (hansi(AT)nordtroms.net), Sep 24 2007
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EXTENSIONS
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Edited by N. J. A. Sloane, Jun 29 2009
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