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 A091308 #15 Apr 15 2024 05:00:39
%S A091308 31,
%T A091308 737169676563615957555351494745434139373533312927252321191715131197531,
%U A091308 12312111911711511311110910710510310199979593918987858381797775737169676563615957555351494745434139373533312927252321191715131197531
%N A091308 Primes in A038395 (concatenate first n odd numbers in reverse order).
%C A091308 Among the first 72 terms only three terms are prime SmBackConOdd(2), SmBackConOdd(37) and SmBackConOdd(62), found by Micha Fleuren.
%C A091308 The next term (a(4)) has 1172 digits. - _Harvey P. Dale_, Jul 12 2022
%C A091308 a(5) = A038395(2717) has 10313 digits. - _Robert Israel_, Apr 14 2024
%H A091308 M. Fleuren, <a href="http://www.gallup.unm.edu/~smarandache/SmBackConOdd.txt">Smarandache Back Concatenated Odds</a>.
%H A091308 Mathematics StackExchange, <a href="https://math.stackexchange.com/questions/4898990/is-it-known-whether-or-not-oeis-sequence-a091308-is-finite">Is it known whether or not OEIS sequence A091308 is finite?</a>
%p A091308 x:= 1: d:= 1: count:= 0: R:= NULL:
%p A091308 for i from 2 while count < 5 do
%p A091308 x:= (2*i-1)*10^d + x;
%p A091308 d:= d + ilog10(2*i-1)+1;
%p A091308 if isprime(x) then count:= count+1; R:= R,x; fi;
%p A091308 od:
%p A091308 R; # _Robert Israel_, Apr 14 2024
%t A091308 Select[Table[FromDigits[Flatten[IntegerDigits/@Range[n,1,-2]]],{n,1,341,2}],PrimeQ] (* _Harvey P. Dale_, Jul 12 2022 *)
%Y A091308 Cf. A038395.
%K A091308 nonn,bref,base
%O A091308 1,1
%A A091308 M. Grete (martha.grete(AT)web.de), Feb 21 2004
%E A091308 Definition corrected by _XU Pingya_, Mar 16 2017