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

1,1

Links

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

Formula

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

Example

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

Mathematica

<<NumberTheory`NumberTheoryFunctions` sz[x_] :=FromDigits[Flatten[Table[IntegerDigits[Prime[j]], {j, 1, x}], 1]] Table[Max[PrimeFactorList[sz[w]]], {w, 1, 25}] (* Labos Elemer, Mar 18 2005 *)
Table[FactorInteger[FromDigits[Flatten[IntegerDigits/@Prime[ Range[n]]]]][[-1, 1]], {n, 25}] (* Harvey P. Dale, Apr 27 2015 *)

Prog

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

Crossrefs

Cf. A019518.

Sequence in context: A049592 A054679 A057621 * A084237 A106928 A070934

Adjacent sequences: A074806 A074807 A074808 * A074810 A074811 A074812

Keyword

nonn,base

Author

Jason Earls, Sep 08 2002

Extensions

More terms from Labos Elemer, Mar 18 2005

Edited by Charles R Greathouse IV, Apr 23 2010

Status

approved