This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A180844 #15 Jun 30 2023 16:28:55 %S A180844 0,1,29,787,21257,573955,15496817,418414123,11297181449,305023899379, %T A180844 8235645283745,222362422662139,6003785411879801,162102206120758723, %U A180844 4376759565260493713,118172508262033346635,3190657723074900391913 %N A180844 a(n) = (27^n - 2^n)/25. %C A180844 The a(n+1) appear in several triangle sums of Nicomachus's table A036561, i.e., Ca2(3*n), Ca2(3*n+1)/3, Ca2(3*n+2)/9 and Ca3(n). See A180662 for information about these camel sums and other chess sums. %H A180844 <a href="/index/Rec#order_02">Index entries for linear recurrences with constant coefficients</a>, signature (29, -54). %F A180844 a(n) = (27^n - 2^n)/25. %F A180844 G.f.: x/((27*x-1)*(2*x-1)). %t A180844 (#[[1]]-#[[2]])/25&/@Partition[Riffle[27^Range[0,20],2^Range[0,20]],2] (* _Harvey P. Dale_, Jan 22 2011 *) %o A180844 (PARI) a(n) = (27^n - 2^n)/25 \\ _Iain Fox_, Dec 12 2017 %o A180844 (PARI) first(n) = Vec(x/((27*x-1)*(2*x-1)) + O(x^n), -n) \\ _Iain Fox_, Dec 12 2017 %Y A180844 Cf. A016153, A016140, A180844, A180845, A180846, A180847, A016185. %K A180844 easy,nonn %O A180844 0,3 %A A180844 _Johannes W. Meijer_, Sep 21 2010