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 A109837 #16 Mar 11 2023 18:05:33
%S A109837 31,3,17,7,3,1579,17,3,2677,131,3,54049423,47,3,487,25541,3,7,211,3,
%T A109837 31,622639,3,498508631,7,3,1259,193,3,7669,16229,3,13,887377,3,
%U A109837 737169676563615957555351494745434139373533312927252321191715131197531
%N A109837 Smallest prime factor of the reverse concatenation of the first n odd numbers.
%C A109837 Sequence starts with offset 2 since A038395(1)=1 has no prime factor. - _M. F. Hasler_
%C A109837 Starting with 2nd term each 3rd term is a(3m)=3.
%C A109837 Sequence A089922={3,73,123,817,...} lists the largest odd number (2n-1) used in the terms a(n) which are primes or probable primes.
%H A109837 Sean A. Irvine, <a href="/A109837/b109837.txt">Table of n, a(n) for n = 2..103</a>
%F A109837 a(n) = A020639(A038395(n)). - _R. J. Mathar_, Sep 16 2007
%e A109837 n=6: a(6)=1579 because 131197531=1579*83089.
%t A109837 s=1;Do[news=FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[s]}]];fi=FactorInteger[news][[1, 1]];Print[fi];s=news, {n, 3, 70, 2}]
%o A109837 (PARI) t=1; for( n=2,99, print1( factor( eval( t=Str( 2*n-1,t)))[1,1],", ")) \\ _M. F. Hasler_, Apr 13 2008
%Y A109837 Cf. A038395, A089922, A104644, A138965.
%K A109837 base,nonn
%O A109837 2,1
%A A109837 _Zak Seidov_, Jul 04 2005
%E A109837 More terms from _R. J. Mathar_, Sep 16 2007
%E A109837 Edited by _M. F. Hasler_, Apr 14 2008
%E A109837 Edited by _T. D. Noe_, Oct 30 2008