A074836 a(1) = 1, a(n) = the largest prime divisor of concatenation of sequence (n,n-1,..,2,1,2,..,n-1,n) A007942.

1, 53, 353, 2160617, 479, 146053847, 18533465459, 18588601, 444444443, 10987654321234567891, 41824630287288128897, 24899126702236725259, 131211109876543212345678910111213, 59722151033999393, 1081735780698166140181, 40378532802777469135803086419727527803285379

Offset: 1

Author

Jason Earls, Sep 09 2002

Keywords

• nonn
• base

Examples

			a(4) is 2160617 because 4321234 = 2.'2160617'.
		

Links

• Sean A. Irvine, Table of n, a(n) for n = 1..55
• M. Fleuren, Smarandache Mirror Sequence.

Crossrefs

Cf. A007942.

Programs

Mathematica

Table[FactorInteger[FromDigits[Join[Flatten[IntegerDigits/@ Range[ n,1,-1]],Flatten[IntegerDigits/@Range[2,n]]]]][[-1,1]],{n,2,15}] (* Harvey P. Dale, Sep 05 2015 *)

Extensions

Edited by Charles R Greathouse IV, Apr 28 2010

More terms from Harvey P. Dale, Sep 05 2015

a(1)=1 inserted by Sean A. Irvine, Jan 30 2025