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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
 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, 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, 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 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,4 COMMENTS Conjecture: a(2) is the only 0 in this sequence. LINKS Table of n, a(n) for n=1..98. EXAMPLE 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). MATHEMATICA 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 *) CROSSREFS Sequence in context: A366852 A318666 A301391 * A343388 A133009 A210705 Adjacent sequences: A068693 A068694 A068695 * A068697 A068698 A068699 KEYWORD base,easy,nonn AUTHOR Amarnath Murthy, Mar 03 2002 EXTENSIONS More terms from Eli McGowan (ejmcgowa(AT)mail.lakeheadu.ca), May 06 2002 Corrected and extended by Jason Earls, Sep 06 2002 STATUS approved

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Last modified June 14 05:27 EDT 2024. Contains 373393 sequences. (Running on oeis4.)