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 A374749 #61 Oct 01 2024 16:18:10
%S A374749 0,9,18,108,279,1260,3780,15129,49158,185328,627759,2295720,7945560,
%T A374749 28607049,100117098,357580548,1258634439,4476859380,15804569340,
%U A374749 56096303769,198337427838,703204161768,2488241012319,8817078468240,31211247579120,110564953793289
%N A374749 Number of zygodrome numbers in base-10 (A033023) with n or fewer digits.
%D A374749 Maarten Looijen, Over getallen gesproken - Talking about numbers, Van Haren Publishing, 2018, page 513.
%H A374749 Giovanni Resta, <a href="http://www.numbersaplenty.com/set/zygodrome/">Zygodrome</a>.
%H A374749 <a href="/index/Rec#order_03">Index entries for linear recurrences with constant coefficients</a>, signature (2,8,-9).
%F A374749 a(n) = A015445(n) - 1.
%F A374749 From _Stefano Spezia_, Sep 07 2024: (Start)
%F A374749 G.f.: 9*x^2/((1 - x)*(1 - x - 9*x^2)).
%F A374749 E.g.f.: exp(x/2)*(cosh(sqrt(37)*x/2) + sinh(sqrt(37)*x/2)/sqrt(37)) - exp(x). (End)
%t A374749 LinearRecurrence[{1, 9}, {1, 10}, 26] - 1 (* _Amiram Eldar_, Sep 06 2024 *)
%o A374749 (PARI) a(n) = ([0, 1; 9, 1]^n)[2, 2] - 1;
%Y A374749 Cf. A015445, A033023.
%K A374749 nonn,easy,base
%O A374749 1,2
%A A374749 _Ruud H.G. van Tol_, Sep 06 2024