Search: id:A121601
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%I A121601
%S A121601 2,6,1,3,1,2,5,9,2,9,7,5,2,7,5,3,0,5,5,7,1,3,2,8,6,3,4,6,8,5,4,3,7,4,3,
%T A121601 0,7,1,6,7,5,2,2,3,7,6,6,9,8,5,3,9,0,5,5,0,9,7,7,9,6,7,3,3,8,1,6,1,6,2,
%U A121601 0,8,2,9,2,2,3,8,4,1,0,1,9,0,3,7,0,7,4,4,0,3,8,5,2,5,6,2,8,6,4,9,2,7,7
%N A121601 Decimal expansion of cosecant of 22.5 degrees = csc(Pi/8).
%C A121601 Also, decimal expansion of 2*sqrt(2)*cos(Pi/8).
%C A121601 1 + csc(Pi/8) is the radius of the smallest circle into which 9 unit 
               circles can be packed ("r=3.613+ Proved by Pirl in 1969.", according 
               to the Friedman link, which has a diagram). csc(Pi/8) is the distance 
               between the center of the larger circle and the center of each unit 
               circle that touches the larger circle.
%D A121601 D. Mumford et al., Indra's Pearls, Cambridge 2002; see p. 362. [From 
               njas, Nov 22 2009]
%e A121601 2.6131259297527530557132863468543743071675223766985390550977...
%o A121601 (PARI) 1/sin(Pi/8)
%Y A121601 Cf. A121598.
%Y A121601 Sequence in context: A024573 A078434 A021892 this_sequence A122761 A100469 
               A124320
%Y A121601 Adjacent sequences: A121598 A121599 A121600 this_sequence A121602 A121603 
               A121604
%K A121601 cons,nonn,new
%O A121601 1,1
%A A121601 Rick L. Shepherd (rshepherd2(AT)hotmail.com), Aug 09 2006

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