A331542 - OEIS

%I #15 Jan 25 2020 09:21:57

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

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

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

%N The speed of light in furlongs per fortnight.

%C Arguably the most well known FFF constant. Note that its precise value depends on the definition of the furlong being used. The value given here is using the international definition of the inch which equals 25.4 millimeters, thus one furlong equals 201.168 meters precisely.

%C From _Jianing Song_, Jan 25 2020: (Start)

%C Decimal expansion of 2518256647200000/1397.

%C Period 42: repeat [9, 9, 7, 8, 5, 2, 5, 4, 1, 1, 5, 9, 6, 2, 7, 7, 7, 3, 8, 0, 1, 0, 0, 2, 1, 4, 7, 4, 5, 8, 8, 4, 0, 3, 7, 2, 2, 2, 6, 1, 9, 8] since a(21). (End)

%H Wikipedia, <a href="https://en.wikipedia.org/wiki/FFF_system">FFF System</a>, <a href="https://en.wikipedia.org/wiki/Speed_of_light">Speed of light</a>, <a href="https://en.wikipedia.org/wiki/Furlong">Furlong</a>, <a href="https://en.wikipedia.org/wiki/Fortnight">Fortnight</a>.

%F 1802617499785.2541159627773801002... furlongs/fortnight = (speed of light in meters/second) * (meter-to-furlong conversion) * (seconds/fortnight) = (299792458 meters/second) * (1/201.168 furlongs/meter) * (1209600 seconds/fortnight).

%F a(n) = 9 - a(n-21) for n >= 42. - _Jianing Song_, Jan 25 2020

%Y Cf. A003678, A001356.

%K nonn,cons,less,dumb

%O 13,2

%A _Scott R. Shannon_, Jan 19 2020

%E More terms from _Jianing Song_, Jan 25 2020