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 A010690 Period 2: repeat (1,9). 6
 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, 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, 1, 9, 1, 9, 1, 9, 1, 9, 1, 9, 1, 9, 1 (list; graph; refs; listen; history; text; internal format)
 OFFSET 0,2 COMMENTS Digital roots of the nonzero square triangular numbers. - Ant King, Jan 21 2012 Continued fraction expansion of A176019. - R. J. Mathar, Mar 08 2012 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 LINKS Index entries for linear recurrences with constant coefficients, signature (0,1). FORMULA a(n) = -4*(-1)^n+5 =9*(n mod 2)+(n+1) mod 2. - Paolo P. Lava, Oct 20 2006 G.f.: (1+9x)/((1-x)(1+x)). - R. J. Mathar, Nov 21 2011 MATHEMATICA 5+4*(-1)^# &/@Range[81] (* Ant King, Jan 21 2012 *) PROG (PARI) a(n)=1; if(n%2==1, 9, 1) \\ Felix FrÃ¶hlich, Aug 11 2014 CROSSREFS Cf. A008592, A189976. Sequence in context: A200696 A203130 A209050 * A224835 A280375 A067617 Adjacent sequences:  A010687 A010688 A010689 * A010691 A010692 A010693 KEYWORD nonn,easy AUTHOR STATUS approved

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Last modified July 22 17:02 EDT 2019. Contains 325225 sequences. (Running on oeis4.)