A105532 Decimal expansion of arctan(1/5).

1, 9, 7, 3, 9, 5, 5, 5, 9, 8, 4, 9, 8, 8, 0, 7, 5, 8, 3, 7, 0, 0, 4, 9, 7, 6, 5, 1, 9, 4, 7, 9, 0, 2, 9, 3, 4, 4, 7, 5, 8, 5, 1, 0, 3, 7, 8, 7, 8, 5, 2, 1, 0, 1, 5, 1, 7, 6, 8, 8, 9, 4, 0, 2, 4, 1, 0, 3, 3, 9, 6, 9, 9, 7, 8, 2, 4, 3, 7, 8, 5, 7, 3, 2, 6, 9, 7, 8, 2, 8, 0, 3, 7, 2, 8, 8, 0, 4, 4, 1, 1, 2, 6, 2, 8

Offset

0,2

Links

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

Eric Weisstein's World of Mathematics, Machin-Like Formulas

Formula

4*arctan(1/5) - A105534 = Pi/4 (Machin's formula).

From Amiram Eldar, Aug 04 2020: (Start)

Equals Sum_{k>=0} (-1)^k/((2*k+1) * 5^(2*k+1)) = Sum_{k>=0} (-1)^k/A072172(k).

Equals Sum_{k>=1} arctan(1/(2*(k+2)^2)). (End)

Example

0.197395559849880758370049765194790293447585103787852101517688940241033969...

Mathematica

RealDigits[ArcTan[1/5], 10, 100][[1]] (* Amiram Eldar, Aug 04 2020 *)

Prog

(PARI) atan(1/5) \\ Michel Marcus, Sep 24 2014

Crossrefs

Cf. A003881 (Pi/4), A072172, A105534 (arctan 1/239).

Sequence in context: A060388 A081821 A164102 * A111471 A078527 A092425

Adjacent sequences: A105529 A105530 A105531 * A105533 A105534 A105535

Keyword

cons,nonn

Author

Bryan Jacobs (bryanjj(AT)gmail.com), Apr 12 2005

Extensions

Corrected position of decimal point in example. - R. J. Mathar, Feb 05 2009

Status

approved