

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
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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: A328818 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



