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 A073000 Decimal expansion of arctangent of 1/2. 13
 4, 6, 3, 6, 4, 7, 6, 0, 9, 0, 0, 0, 8, 0, 6, 1, 1, 6, 2, 1, 4, 2, 5, 6, 2, 3, 1, 4, 6, 1, 2, 1, 4, 4, 0, 2, 0, 2, 8, 5, 3, 7, 0, 5, 4, 2, 8, 6, 1, 2, 0, 2, 6, 3, 8, 1, 0, 9, 3, 3, 0, 8, 8, 7, 2, 0, 1, 9, 7, 8, 6, 4, 1, 6, 5, 7, 4, 1, 7, 0, 5, 3, 0, 0, 6, 0, 0, 2, 8, 3, 9, 8, 4, 8, 8, 7, 8, 9, 2, 5, 5, 6, 5, 2, 9 (list; constant; graph; refs; listen; history; text; internal format)
 OFFSET 0,1 COMMENTS The angle at which you must shoot a cue ball on a standard pool table so that it will strike all four sides and return to its origin. [Barrow] - Robert G. Wilson v, Nov 29 2015 REFERENCES John D. Barrow, One Hundred Essential Things You Didn't Know You Didn't Know, W. W. Norton & Co., NY & London, 2008. LINKS G. C. Greubel, Table of n, a(n) for n = 0..5000 P. Bala, New series for old functions R. J. Mathar, Hierarchical Subdivision of the Simple Cubic Lattice, arXiv preprint arXiv:1309.3705 [math.MG], 2013. Simon Plouffe, arctan(1/2) FORMULA Equals Pi/2 - A105199 = A019669 - A105199. - R. J. Mathar, Aug 21 2013 From Peter Bala, Feb 04 2015: (Start) Arctan(1/2) = 1/2*Sum_{k >= 0} (-1)^k/((2*k + 1)*4^k). Define a pair of integer sequences A(n) = 4^n*(2*n + 1)!/n! and B(n) = A(n)*Sum_{k = 0..n} (-1)^k/((2*k + 1)*4^k). Both sequences satisfy the same second order recurrence equation u(n) = (12*n + 10)*u(n-1) + 16*(2*n - 1)^2*u(n-2). From this observation we obtain the continued fraction expansion 2*arctan(1/2) = 1 - 2/(24 + 16*3^2/(34 + 16*5^2/(46 + ... + 16*(2*n - 1)^2/((12*n + 10) + ...)))). See A002391, A105531 and A002162 for similar expansions. Arctan(1/2) = 2/5 * Sum_{k >= 0} (4/5)^k/((2*k + 1)*binomial(2*k,k)). Define a pair of integer sequences C(n) = 5^n*(2*n + 1)!/n! and D(n) = C(n)*Sum_{k = 0..n} (4/5)^k/((2*k + 1)*binomial(2*k,k)). Both sequences satisfy the same second order recurrence equation u(n) = (24*n + 10)*u(n-1) - 40*n*(2*n - 1)^2*u(n-2). From this observation we obtain the continued fraction expansion 5/2*arctan(1/2) = 1 + 4/(30 - 240/(58 - 600/(82 - ... - 40*n*(2*n - 1)/((24*n + 10) - ... )))). Arctan(1/2) = 2/25 * Sum_{k >= 0} (24*k + 17)*(4/5)^(2*k)/( (4*k + 1)*(4*k + 3)*binomial(4*k,2*k) ). Arctan(1/2) = 2/125 * Sum_{k >= 0} (1116*k^2 + 1446*k + 433)*(4/5)^(3*k)/( (6*k + 1)*(6*k + 3)*(6*k + 5)*binomial(6*k,3*k) ). (End) EXAMPLE Arctan(1/2) =0.463647609000806116214256231461214402028537054286120263810933088720197864165... radians =26°.56505117707798935157219372045329467120421429964522102798601631528806582148474... =26°33'.9030706246793610943316232271976802722528579787132616791609789172839492890... =26°33'54".184237480761665659897393631860816335171478722795700749658735037036957... complement = 63°.43494882292201064842780627954670532879578570035477897201398368471... supplement = 153°.4349488229220106484278062795467053287957857003547789720139836847... MAPLE evalf(arctan(0.5)) ; # R. J. Mathar, Aug 22 2013 MATHEMATICA RealDigits[ ArcTan[1/2], 10, 110] [[1]] PROG (PARI) default(realprecision, 2000); atan(1/2) \\ Anders Hellström, Nov 30 2015 CROSSREFS Cf. A002162, A002391, A105531, A254619. Sequence in context: A179453 A273819 A276761 * A198113 A264962 A082193 Adjacent sequences:  A072997 A072998 A072999 * A073001 A073002 A073003 KEYWORD cons,nonn AUTHOR Robert G. Wilson v, Aug 03 2002 STATUS approved

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Last modified October 16 13:21 EDT 2019. Contains 328083 sequences. (Running on oeis4.)