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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
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
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.)