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 A107273 #15 Jul 12 2022 18:07:44 %S A107273 10011001,10025001,10052001,10088001,10100101,10111101,10125101, %T A107273 10152101,10188101,10200501,10211501,10225501,10252501,10288501, %U A107273 11011011,11025011,11052011,11088011,11100111,11111111,11125111 %N A107273 Vertically symmetrical dates MMDDYYYY (American notation) excluding years which are divisible by 10, considered as numbers, in increasing order. %C A107273 2 and 5 are taken as mirror images (as on calculator displays). a(1)=10011001 and a(20)=11111111 shared the property to present also two symmetrical halves. %C A107273 This sequence has exactly 42 terms, ending with 12288551 (Dec. 28th 8551). %H A107273 Iain Fox, <a href="/A107273/b107273.txt">Table of n, a(n) for n = 1..42</a> %o A107273 (PARI) a(n) = my(d=digits(126+25*((n-1)\14)+(n-1)%14, 5)); fromdigits(apply(i->[0, 1, 2, 5, 8, 5, 2][i+1], concat(d, apply(i->i+3*bitand(i, 2)/2, Vecrev(d))))) \\ _Iain Fox_, Jul 08 2022 %Y A107273 Condensed American notation dates: A107274. %Y A107273 Metric convention dates: A107275. %Y A107273 Condensed European notation dates: A107276. %Y A107273 Cf. A053701, A106605. %K A107273 base,easy,fini,full,nonn %O A107273 1,1 %A A107273 _Alexandre Wajnberg_, May 19 2005 %E A107273 Definition clarified by _Hieronymus Fischer_, Apr 01 2012