%I #15 Feb 27 2022 05:46:12
%S 1,12,105,360,858,1680,2907,4620,6900,9828,13485,17952,23310,29640,
%T 37023,45540,55272,66300,78705,92568,107970,124992,143715,164220,
%U 186588,210900,237237,265680,296310,329208,364455,402132,442320,485100,530553,578760,629802
%N a(0)=1, a(n) = (3n-1)*3n*(3n+1)/2 for n>0.
%F Sum_{n>=0} 1/a(n) = log(3).
%F G.f.: (1+8x+63x^2+8x^3+x^4)/(1-x)^4.
%F a(n) = A027480(3n-1), n>0. - _R. J. Mathar_, Apr 07 2009
%F Sum_{n>=0} (-1)^n/a(n) = 4*log(2)/3. - _Amiram Eldar_, Feb 27 2022
%t nxt[{n_,a_}]:={n+1,((3n)(3n-1)(3n+1))/2}; NestList[nxt,{0,1},40][[All,2]]/.(0->Nothing) (* _Harvey P. Dale_, Sep 24 2016 *)
%Y Cf. A002391, A027480, A058962, A097321, A154920.
%K nonn
%O 0,2
%A _Jaume Oliver Lafont_, Feb 21 2009
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