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 A272615 #10 May 03 2016 17:04:54 %S A272615 0,1,2,3,4,8,12,63,240 %N A272615 Numbers with digits in descending numerical order in base 2, 3 and 4 expansions. %C A272615 a(10), if it exists, has more than 1000 decimal digits. Conjecture: there are no more terms in this sequence. - _Charles R Greathouse IV_, May 03 2016 %e A272615 12 is 1100 in base 2, 110 in base 3 and 30 in base 4; in each representation every digit is smaller than or equal to the one proceeding so 12 is a term. %e A272615 Similarly, 63 is 111111 in base 2, 2100 in base 3 and 333 in base 4 so it is also a term. %o A272615 (PARI) dec(n,b)=my(v=digits(n,b)); v==vecsort(v,,4) %o A272615 is(n)=dec(n,2) && dec(n,3) && dec(n,4) \\ _Charles R Greathouse IV_, May 03 2016 %o A272615 (PARI) dec(n,b)=my(v=digits(n,b)); v==vecsort(v,,4) %o A272615 list(lim)=my(v=List([0]),t); for(i=1,logint(lim\1+1,4), t=4^i-1; while(t<=lim, if(dec(t,3), listput(v,t)); t*=4); t=2*4^i-2; while(t<=lim, if(dec(t,3), listput(v,t)); t*=4)); Set(v) \\ _Charles R Greathouse IV_, May 03 2016 %Y A272615 Intersection of A023758, A023759, and A023760. %K A272615 nonn,base %O A272615 1,3 %A A272615 _Robin Powell_, May 03 2016