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 A272264 #21 Dec 01 2018 19:58:53
%S A272264 6,9,16,18,19,61,66,68,81,86,89,91,98,99,106,108,109,116,118,119,161,
%T A272264 166,168,169,186,188,189,191,196,198,199,601,606,608,611,616,618,661,
%U A272264 666,668,669,681,686,688,691,696,698,699,801,806,809,811,816,819,861,866,868,869,881,886,889
%N A272264 Numbers that become a different number when flipped upside down.
%C A272264 Although 2 and 5 flipped upside down on a digital clock are numbers, they are not permitted here. - _David A. Corneth_, May 22 2016
%H A272264 A. D. Skovgaard, <a href="/A272264/b272264.txt">Table of n, a(n) for n = 1..10000</a>
%o A272264 (PARI) is(n) = {my(d=digits(n),dr); if(d[#d]==0 || #setminus(Set(d),Set([0,1,6,8,9])) !=0, return(0), dr=vector(#d)); for(i=1,#d, dr[#d-i+1] = if(d[i]==6||d[i]==9,15-d[i],d[i]));dr!=d} \\ _David A. Corneth_, May 22 2016
%Y A272264 Cf. A000787, A045574.
%K A272264 base,easy,nonn
%O A272264 1,1
%A A272264 _A. D. Skovgaard_, Apr 24 2016