Search: id:A048907
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%I A048907
%S A048907 1,10,154,2449,39025,621946,9912106,157971745,2517635809,40124201194,
%T A048907 639469583290,10191389131441,162422756519761,2588572715184730,
%U A048907 41254740686435914,657487278267789889,10478541711598202305
%N A048907 Indices of 9-gonal numbers which are also triangular.
%C A048907 Entries are == 1 (mod 3). - N. J. A. Sloane (njas(AT)research.att.com), 
               Sep 22, 2007
%H A048907 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 A048907 G.f.: [1-7x+x^2]/[(1-x)(1-16x+x^2)].
%F A048907 a(n+2)=16*a(n+1)-a(n)-5, a(n+1)=8*a(n)-2.5+1.5*(28*a(n)^2-20*a(n)+1)^0.5 
               - Richard Choulet (richardchoulet(AT)yahoo.fr), Sep 22 2007
%F A048907 a(n)=(5/14)+(9/28)*{[8-3*sqrt(7)]^n+[8+3*sqrt(7)]^n}+(3/28)*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 A048907 Cf. A001080, A073352, A048908, A048909.
%Y A048907 Cf. A048909 A048908.
%Y A048907 Sequence in context: A116156 A025750 A034325 this_sequence A061654 A087603 
               A129460
%Y A048907 Adjacent sequences: A048904 A048905 A048906 this_sequence A048908 A048909 
               A048910
%K A048907 nonn
%O A048907 1,2
%A A048907 Eric Weisstein (eric(AT)weisstein.com)

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