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

1,1

Links

Table of n, a(n) for n=1..17.

Example

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

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 *)

Crossrefs

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

Sequence in context: A327447 A139954 A153636 * A108293 A316349 A063339

Adjacent sequences: A109837 A109838 A109839 * A109841 A109842 A109843

Keyword

base,nonn

Author

Zak Seidov, Jul 05 2005

Status

approved