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 A341705 #9 Mar 07 2021 19:49:23 %S A341705 1,1,1,1,3,11,31,71,211,883,3571,12211,35641,91521,212213,453181, %T A341705 904541,1706461,3069181,5298493,8827591,14256271,22398531,34339691, %U A341705 51504223,75735551,109389151,155440351,217608301,300497653,409759561,552273681,736352921,971972761 %N A341705 a(n) = 70*binomial(n,8) + 2*binomial(n,4) + 1. %C A341705 a(n) is the number of ternary strings of length n that contain either none or four 0's and either none or four 1's. %H A341705 <a href="/index/Rec#order_09">Index entries for linear recurrences with constant coefficients</a>, signature (9,-36,84,-126,126,-84,36,-9,1). %F A341705 E.g.f.: exp(x)*(1 + x^4/24)^2. %F A341705 O.g.f.:(1 - 8*x + 28*x^2 - 56*x^3 + 72*x^4 - 64*x^5 + 40*x^6 - 16*x^7 + 73*x^8)/(1 - x)^9. - _Stefano Spezia_, Feb 19 2021 %e A341705 a(9)=883 since the strings are the 630 permutations of 000011112, the 126 permutations of 000022222, the 126 permutations of 111122222, and 222222222. %Y A341705 Cf. A341703, A341704. %K A341705 nonn,easy %O A341705 0,5 %A A341705 _Enrique Navarrete_, Feb 17 2021