%I A048908
%S A048908 1,25,406,6478,103249,1645513,26224966,417953950,6661038241,
%T A048908 106158657913,1691877488374,26963881156078,429730221008881,
%U A048908 6848719654986025,109149784258767526,1739547828485294398
%N A048908 Indices of triangular numbers which are also 9-gonal.
%H A048908 Eric Weisstein's World of Mathematics, <a href="http://mathworld.wolfram.com/
               NonagonalTriangularNumber.html">Link to a section of The World of 
               Mathematics.</a>
%F A048908 a(n+2)=16*a(n+1)-a(n)+7, a(n+1)=8*a(n)+3.5+1.5*(28*a(n)^2+28*a(n)+25)^0.5 
               - Richard Choulet (richardchoulet(AT)yahoo.fr), Sep 22 2007
%F A048908 G.f.: f(z)=a(1)*z+a(2)*z^2+...= (z+8z^2-2*z^3)/((1-z)*(1-16*z+z^2)) - 
               R. Choulet (richardchoulet(AT)yahoo.fr), Oct 09 2007
%F A048908 a(n)=-(1/2)+(3/4)*{[8-3*sqrt(7)]^n+[8+3*sqrt(7)]^n}+(9/28)*sqrt(7)*{[8+3*sqrt(7)]^n- 
               [8-3*sqrt(7)]^n}, with n>=0 [From Paolo P. Lava (ppl(AT)spl.at), 
               Nov 25 2008]
%Y A048908 Cf. A048907, A048909.
%Y A048908 Sequence in context: A028064 A028061 A026561 this_sequence A026391 A028044 
               A028057
%Y A048908 Adjacent sequences: A048905 A048906 A048907 this_sequence A048909 A048910 
               A048911
%K A048908 nonn
%O A048908 1,2
%A A048908 Eric Weisstein (eric(AT)weisstein.com)