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a[n] is the largest prime before A002278[n] repdigits.
1

%I #6 Oct 15 2013 22:32:36

%S 3,43,443,4441,44417,444443,4444409,44444399,444444443,4444444429,

%T 44444444441,444444444443,4444444444439,44444444444353,

%U 444444444444421,4444444444444423,44444444444444411,444444444444444419

%N a[n] is the largest prime before A002278[n] repdigits.

%H Harvey P. Dale, <a href="/A099664/b099664.txt">Table of n, a(n) for n = 1..1000</a>

%e n=2: 43 is before 44.

%t <<NumberTheory`NumberTheoryFunctions` Table[Table[PreviousPrime[4*(10^n-1)/9], {n, 1, 35}]

%t Table[NextPrime[FromDigits[PadRight[{},n,4]],-1],{n,20}] (* _Harvey P. Dale_, Feb 25 2013 *)

%Y Cf. A003618, A003617, A096497, A096498, A068104, A002275-A002283, A099656-A099668.

%K base,nonn

%O 1,1

%A _Labos Elemer_, Nov 17 2004