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Search: id:A001539
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| 3, 35, 99, 195, 323, 483, 675, 899, 1155, 1443, 1763, 2115, 2499, 2915, 3363, 3843, 4355, 4899, 5475, 6083, 6723, 7395, 8099, 8835, 9603, 10403, 11235, 12099, 12995, 13923, 14883, 15875, 16899, 17955
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OFFSET
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0,1
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COMMENT
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Sequence arises from reading the line from 3, in the direction 3, 35,... in the square spiral whose vertices are the squares A000290. - Omar E. Pol (info(AT)polprimos.com), May 24 2008
(log(sq(2)+1))/sqrt(2) = .62322524...= 2/3 - 2/35 + 2/99 - 2/195 + 2/323,...; = (1 - 1/3) + (1/7 - 1/5) + (1/9 - 1/11) + (1/15 - 1/13) + (1/17 - 1/19) + (1/23 - 1/21) + ... [From Gary W. Adamson (qntmpkt(AT)yahoo.com), Mar 01 2009]
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FORMULA
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Sum(k>=0, 1/a(k)) = Pi/8 - Benoit Cloitre (benoit7848c(AT)orange.fr), Aug 20 2002
G.f.: (3+26*x+3*x^2)/(1-x)^3 [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 07 2009]
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CROSSREFS
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a(n) = A016826(n) - 1 = [A001533(n)+5]/4 = [A001538(n)+16]/9. Bisection of A000466.
Cf. A000290, A016286.
Cf. A157142, A133766, A154633. [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), Mar 07 2009]
Sequence in context: A054783 A102104 A054287 this_sequence A113854 A076376 A133710
Adjacent sequences: A001536 A001537 A001538 this_sequence A001540 A001541 A001542
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KEYWORD
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nonn,easy
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AUTHOR
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N. J. A. Sloane (njas(AT)research.att.com).
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