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A010690 Period 2: repeat (1,9). 2
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; internal format)
OFFSET

0,2

COMMENTS

Digital roots of the non-zero square triangular numbers.  - Ant King, Jan 21 2012

LINKS

Index to sequences with 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 (paoloplava(AT)gmail.com), 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 *)

CROSSREFS

Sequence in context: A175615 A200696 A203130 * A067617 A021525 A197724

Adjacent sequences:  A010687 A010688 A010689 * A010691 A010692 A010693

KEYWORD

nonn,easy

AUTHOR

N. J. A. Sloane (njas(AT)research.att.com).

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Last modified February 16 06:18 EST 2012. Contains 205860 sequences.