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 A068696 Number of primes that are a concatenation nk of n and k for values of k from 1 to n. 2

%I #10 Dec 15 2017 17:35:50

%S 1,0,1,2,1,1,2,1,1,4,1,1,3,1,3,3,2,2,5,2,3,5,3,4,3,4,5,3,3,4,5,3,7,4,

%T 7,5,5,5,7,6,6,7,6,5,5,7,5,4,7,6,3,6,4,10,5,8,8,9,6,8,9,6,10,7,8,6,7,

%U 8,8,9,6,9,8,7,12,8,8,9,8,7,9,13,8,8,12,10,11,13,8,9,11,9,11,15,8,12,13,12

%N Number of primes that are a concatenation nk of n and k for values of k from 1 to n.

%C Conjecture: a(2) is the only 0 in this sequence.

%e a(33)= 7 as we get primes 331, 337, 3313, 3319, 3323, 3329, 3331, for seven values of k i.e. k = 1, 7, 13, 19, 23, 29, 31. a(20) = 2, the primes are 2011 and 2017 (2003 doesn't count).

%t d[n_]:=IntegerDigits[n]; Table[c=0; Do[If[PrimeQ[FromDigits[Join[d[n],d[k]]]],c=c+1],{k,n}]; c,{n,98}] (* _Jayanta Basu_, May 21 2013 *)

%K base,easy,nonn

%O 1,4

%A _Amarnath Murthy_, Mar 03 2002

%E More terms from Eli McGowan (ejmcgowa(AT)mail.lakeheadu.ca), May 06 2002

%E Corrected and extended by _Jason Earls_, Sep 06 2002

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Last modified July 22 23:01 EDT 2024. Contains 374544 sequences. (Running on oeis4.)