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A073000 Decimal expansion of arctangent of 1/2. 10
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

LINKS

Table of n, a(n) for n=0..104.

P. Bala, New series for old functions

R. J. Mathar, Hierarchical Subdivision of the Simple Cubic Lattice, arXiv preprint arXiv:1309.3705, 2013

Simon Plouffe, arctan(1/2)

FORMULA

Equals Pi/2 - A105199 = A019669 - A105199. - R. J. Mathar, Aug 21 2013

From Peter Bala, Feb 04: (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

Atan(0.5) = 0.463647609000806... rad = 26.5650511770779.. deg, 180-deg complement to 153.4349488... deg.

MAPLE

evalf(arctan(0.5)) ; # R. J. Mathar, Aug 22 2013

MATHEMATICA

RealDigits[ ArcTan[1/2], 10, 110] [[1]]

CROSSREFS

Cf. A002162, A002391, A105531, A254619.

Sequence in context: A081709 A200640 A179453 * A198113 A082193 A255767

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 September 1 22:41 EDT 2015. Contains 261279 sequences.