login
1 followed by infinitely many 9's.
0

%I #28 Jan 18 2024 09:33:50

%S 1,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,

%T 9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,

%U 9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9,9

%N 1 followed by infinitely many 9's.

%C The digital root of 9^(n-1). - _Cino Hilliard_, Dec 31 2004

%C With interpolated zeros (1,0,9,0,9,0,9,0,...) this is the number of hours between times when the hands of a two-handed clock cross. - _Halfdan Skjerning_, Aug 18 2017

%H Brady Haran and Cliff Stoll, <a href="https://www.youtube.com/watch?v=HcqdqsQq-6M">When do clock hands overlap?</a>, Numberphile video (2017)

%H <a href="/index/Rec#order_01">Index entries for linear recurrences with constant coefficients</a>, signature (1).

%F G.f.: x*(1 + 8*x)/(1 - x). - _Chai Wah Wu_, Aug 19 2017

%F E.g.f.: 9*(exp(x) - 1) - 8*x. - _Stefano Spezia_, Oct 16 2023

%t PadRight[{1},100,9] (* _Paolo Xausa_, Oct 16 2023 *)

%Y Cf. A178181, A010734, A180599, A100403, A100401.

%K nonn,easy

%O 1,2

%A _N. J. A. Sloane_, Aug 19 2017