A074809 Largest prime factor of A019518, concatenation of first n primes.

2, 23, 47, 2357, 223, 35339, 214282847, 7717859, 806801, 185176472401, 357211, 4967701595369, 104364752351, 27558919, 5269410931806332951, 274784055330749, 1191126125288819, 178258515898000387, 2313161253378144566969023310693, 8730041915527145606449758346652473, 26293517701186435480644832888393, 29890227360205834316383307128051, 3858432486690092813, 7122852423207105431971, 93753283248830261744671

Offset: 1

Author

Jason Earls, Sep 08 2002

Keywords

• nonn
• base

Examples

			For n=5: concatenation of {2,3,5,7,11} is 235711 = 7*151*223, largest prime divisor is a(5)=223.
		

Links

• Daniel Suteu, Table of n, a(n) for n = 1..69

Crossrefs

Cf. A019518.

Programs

Mathematica

<Labos Elemer, Mar 18 2005 *)
Table[FactorInteger[FromDigits[Flatten[IntegerDigits/@Prime[ Range[n]]]]][[-1,1]],{n,25}] (* Harvey P. Dale, Apr 27 2015 *)

PARI

a(n) = vecmax(factor(eval(concat(apply(s->Str(s), primes(n)))))[,1]); \\ Daniel Suteu, May 26 2022

Formula

a(n) = A006530(A019518(n)). - Daniel Suteu, May 26 2022

Extensions

More terms from Labos Elemer, Mar 18 2005

Edited by Charles R Greathouse IV, Apr 23 2010