%I A072172
%S A072172 5,375,15625,546875,17578125,537109375,15869140625,457763671875,12969970703125,
%T A072172 362396240234375,10013580322265625,274181365966796875,7450580596923828125,
%U A072172 201165676116943359375,5401670932769775390625,144354999065399169921875
%N A072172 (2*n+1)*5^(2*n+1).
%C A072172 J. Machin (died 1751) used Pi/4 = 4*Sum_{n=0..inf} (-1)^n/((2*n+1)*5^(2*n+1)) 
               - Sum_{n=0..inf} (-1)^n/((2*n+1)*239^(2*n+1)) to calculate Pi to 
               100 decimal places.
%D A072172 H. Doerrie, 100 Great Problems of Elementary Mathematics, Dover, NY, 
               1965, p. 73
%Y A072172 Cf. A072173.
%Y A072172 Cf. A157332. [From Jaume Oliver Lafont (joliverlafont(AT)gmail.com), 
               Mar 03 2009]
%Y A072172 Sequence in context: A121668 A160193 A098038 this_sequence A100474 A152438 
               A060506
%Y A072172 Adjacent sequences: A072169 A072170 A072171 this_sequence A072173 A072174 
               A072175
%K A072172 nonn
%O A072172 0,1
%A A072172 N. J. A. Sloane (njas(AT)research.att.com), Jun 30 2002