%I #5 Sep 02 2023 15:29:23

%S 31,59,443,13933,2609,83089,18937669,57697,71615663503,

%T 161768817795401,4356390089,4668342004597,109230695824219,

%U 2770122504473483,217596035578054625221,1721572826917,659160492491

%N Largest prime factor of the reverse concatenation of the first n consecutive odd numbers.

%e n = 6: a(6) = 83089 because 131197531 = 1579 * 83089.

%t s=1;ss={};Do[news=FromDigits[Flatten[{IntegerDigits[n], IntegerDigits[s]}]];fi=FactorInteger[news][[ -1, 1]];s=news;AppendTo[ss, fi], {n, 3, 60, 2}]; A109840=ss

%t With[{nn=17},Table[FactorInteger[FromDigits[Flatten[IntegerDigits/@Reverse[Range[1,2n+1,2]]]]][[-1,1]],{n,nn}]] (* _Harvey P. Dale_, Sep 02 2023 *)

%Y Cf. A109837 = smallest prime factor of the reverse concatenation of the first n consecutive odd numbers.

%K base,nonn

%O 1,1

%A _Zak Seidov_, Jul 05 2005