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%I #44 Feb 21 2024 10:52:46
%S 1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,
%T 1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,1,9,
%U 1,9,1,9,1,9,1,9,1,9,1,9,1
%N Period 2: repeat (1,9).
%C Digital roots of the nonzero square triangular numbers. - _Ant King_, Jan 21 2012
%C Continued fraction expansion of A176019. - _R. J. Mathar_, Mar 08 2012
%C Exp( Sum_{n >= 1} a(n-1)*x^n/n ) = 1 + x + 5*x^2 + 5*x^3 + 15*x^4 + 15*x^5 + ... is the o.g.f. for A189976 (taken with an offset of 0). - _Peter Bala_, Mar 13 2015
%C Final digit of 9^n. - _Martin Renner_, Jun 11 2020
%H <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (0,1).
%F G.f.: (1+9x)/((1-x)(1+x)). - _R. J. Mathar_, Nov 21 2011
%F a(n) = 9^n mod 10. - _Martin Renner_, Jun 11 2020
%t 5+4*(-1)^# &/@Range[81] (* _Ant King_, Jan 21 2012 *)
%o (PARI) a(n)=1; if(n%2==1, 9, 1) \\ _Felix Fröhlich_, Aug 11 2014
%Y Cf. A008592, A001019 (9^n), A014393, A189976.
%K nonn,easy
%O 0,2
%A _N. J. A. Sloane_
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