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 A111677 Array of primes of the type k concatenated with 2n-1 where k < 2n-1. 1---> no prime 13,23 5---> no prime 17,37,47,67 19,29,59,79,89 211,311,811,911 113,313,613,1013,1213 15---> no prime 317,617,... ... Sequence contains the number of terms in the n-th rows. 2

%I

%S 0,2,0,4,5,4,5,0,4,7,7,9,0,8,9,12,10,0,12,14,11,12,0,16,15,19,17,0,23,

%T 18,17,20,0,22,19,22,23,0,24,25,25,26,0,26,27,28,30,0,29,28,25,29,0,

%U 28,28,26,23,0,24,33,33,30,0,28,30,33,26,0,25,34,27,32,0,32,34,35,42,0,33

%N Array of primes of the type k concatenated with 2n-1 where k < 2n-1. 1---> no prime 13,23 5---> no prime 17,37,47,67 19,29,59,79,89 211,311,811,911 113,313,613,1013,1213 15---> no prime 317,617,... ... Sequence contains the number of terms in the n-th rows.

%C Conjecture: a(n)=0 iff n== 3 (mod 5). [Corrected by _R. J. Mathar_, Aug 20 2007]

%C Subsidiary sequences: (1) First occurrence of n in A111677. There are numbers like 3 which probably do not occur in this sequence, let a(3) = -1. (2) Terms that do not occur in A111677.

%e For 2n-1 = 9, we have primes 19,29,59,79 and 89. Hence a(5) = 5.

%p cat2 := proc(n,m) n*10^(max(1,ilog10(m)+1))+m ; end: A111677 := proc(nrow) local town1,k,a ; town1 := 2*nrow-1 ; a := [] ; for k from 1 to town1-1 do if isprime(cat2(k,town1)) then a := [op(a),cat2(k,town1)] ; fi ; od; RETURN(nops(a)) ; end: seq(A111677(nrow),nrow=1..80) ; # _R. J. Mathar_, Aug 20 2007

%Y Cf. A111676.

%K base,nonn

%O 1,2

%A _Amarnath Murthy_, Aug 16 2005

%E More terms from _R. J. Mathar_, Aug 20 2007

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