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[N. J. A. Sloane]

A104643=A074809?
zak

%I A074809
%S A074809
2,23,47,2357,223,35339,214282847,7717859,806801,185176472401,357211,
%T A074809
4967701595369,104364752351,27558919,5269410931806332951,
%U A074809
274784055330749,1191126125288819,178258515898000387,2313161253378144566969023310693,
              
8730041915527145606449758346652473,26293517701186435480644832888393,
              
29890227360205834316383307128051,3858432486690092813,7122852423207105431971,
               93753283248830261744671
%N A074809 Largest prime factor of A019518,
concatenation of first n primes.
%e A074809 n=5: concatenation of {2,3,5,7,11} is
235711=7.151.223, largest prime divisor is 
               a(5)=223.
%t A074809 <<NumberTheory`NumberTheoryFunctions`
sz[x_]
:=FromDigits[Flatten[Table[IntegerDigits[Prime[j]], 
               {j, 1, x}], 1]]
Table[Max[PrimeFactorList[sz[w]]], {w, 1, 25}] (Labos)
%Y A074809 Cf. A019158.
%Y A074809 Adjacent sequences: A074806 A074807 A074808
this_sequence A074810 A074811 A074812
%Y A074809 Sequence in context: A049592 A057621
A104643 this_sequence A084237 A106928 A070934
%K A074809 nonn
%O A074809 1,1
%A A074809 Jason Earls (jcearls(AT)cableone.net), Sep
08 2002
%E A074809 More terms from Labos E.
(labos(AT)ana.sote.hu), Mar 18 2005

%I A104643
%S A104643
2,23,47,2357,223,35339,214282847,7717859,806801,185176472401,357211,
%T A104643
4967701595369,104364752351,27558919,5269410931806332951,
%U A104643
274784055330749,1191126125288819,178258515898000387
%N A104643 a(n) is the largest prime factor of the
number obtained from concatenation of the 
               first n primes.
%e A104643 n=5, concatenation of {2,3,5,7,11} is
235711=7.151.223, largest prime divisor
%e A104643 is a(5)=223.
%t A104643 <<NumberTheory`NumberTheoryFunctions`
sz[x_]
:=FromDigits[Flatten[Table[IntegerDigits[Prime[j]], 
               {j, 1, x}], 1]]
Table[Max[PrimeFactorList[sz[w]]], {w, 1, 25}]
%Y A104643 Cf. A019158.
%Y A104643 Adjacent sequences: A104640 A104641 A104642
this_sequence A104644 A104645 A104646
%Y A104643 Sequence in context: A105440 A049592
A057621 this_sequence A074809 A084237 A106928
%K A104643 nonn
%O A104643 1,1
%A A104643 Labos E. (labos(AT)ana.sote.hu), Mar 18
2005



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