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 A057517 #5 Aug 03 2017 00:41:22 %S A057517 10,44,50,180,184,204,210,226,724,728,740,744,752,820,824,844,850,866, %T A057517 908,914,930,962,2900,2904,2916,2920,2928,2964,2968,2980,2984,2992, %U A057517 3012,3016,3024,3040,3284,3288,3300,3304,3312,3380,3384,3404,3410,3426 %N A057517 Binary encodings of the Catalan mountain ranges with exactly one sea-level valley, i.e., the rooted plane trees with root degree = 2. %C A057517 This bijective mapping from all rooted plane trees to one node larger, root degree = 2 trees illustrates the fact that CONV(A000108, A000108) = LEFT(A000108). (Catalan numbers shift left under convolution). %F A057517 a(n) = alltrees2doubletrunked(A014486(n)) (Starting from n=1). %p A057517 alltrees2doubletrunked := n -> pars2binexp(alltrees2doubletrunkedP(binexp2pars(n))); %p A057517 alltrees2doubletrunkedP := h -> [car(h),cdr(h)]; %Y A057517 Cf. A057501 (for binexp2pars, pars2binexp, car, cdr), A057518, A057519, A057122. Single-trunked trees: A057547. %K A057517 nonn %O A057517 1,1 %A A057517 _Antti Karttunen_, Sep 03 2000