A109840 Largest prime factor of the reverse concatenation of the first n consecutive odd numbers.

31, 59, 443, 13933, 2609, 83089, 18937669, 57697, 71615663503, 161768817795401, 4356390089, 4668342004597, 109230695824219, 2770122504473483, 217596035578054625221, 1721572826917, 659160492491

Offset: 1

Author

Zak Seidov, Jul 05 2005

Keywords

• base
• nonn

Examples

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

Crossrefs

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

Programs

Mathematica

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