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
Final digit of 9^n. - Martin Renner, Jun 11 2020
LINKS
FORMULA
G.f.: (1+9x)/((1-x)(1+x)). - R. J. Mathar, Nov 21 2011
a(n) = 9^n mod 10. - Martin Renner, Jun 11 2020
MATHEMATICA
5+4*(-1)^# &/@Range[81] (* Ant King, Jan 21 2012 *)
PROG
(PARI) a(n)=1; if(n%2==1, 9, 1) \\ Felix Fröhlich, Aug 11 2014
CROSSREFS
KEYWORD
nonn,easy
AUTHOR
STATUS
approved