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

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

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 A384783 A133009

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